ci: Build Docker Hub images using GitHub Actions

[alco]

This reproduces our Buildkite pipeline on GitHub Actions and allows us to retire Buildkite.

The most painful problem that this solves are the missing webhooks that result in missed release images on Docker Hub. In a few words, when we push a release commit to main that touches 4 or more components, and so the commit itself gets 4+ tags, GitHub does not send a webhook to Buildkite because of its limit on max tags. In such cases, we always had to manually force-push only the @core/sync-service:... tag to trigger a Buildkite pipeline.

The GitHub Actions workflow implemented here is verbose because it has to orchestrate a single shared step, followed by a matrix that uses a separate runner for building different platforms, followed by another shared step that collects the digests from the matrix and combines them into a single multi-arch tagged image on Docker Hub.

It may be possible to simplify it later on, since our next target is migrating some or all of our runners to Blacksmith, and Blacksmith promises to implement implicit forking of Docker builder into different runners based on the passed platforms, kinda like Buildkite has been doing.

Closes #3607.

[codecov]

❌ 1 Tests Failed:

Tests completed	Failed	Passed	Skipped
1920	1	1919	0

View the top 2 failed test(s) by shortest run time

Elixir.Electric.Plug.RouterTest::test /v1/shapes - subqueries move-in into move-out into move-in of the same parent results in a 

Stack Traces | 1.32s run time

71) test /v1/shapes - subqueries move-in into move-out into move-in of the same parent results in a  (Electric.Plug.RouterTest)
     .../electric/plug/router_test.exs:2749
     match (=) failed
     code:  assert {_req, 200,
             [
               %{"headers" => %{"event" => "move-out", "patterns" => p1}},
               %{"headers" => %{"event" => "move-out", "patterns" => p1}},
               %{"headers" => %{"control" => "snapshot-end"}},
               %{
                 "headers" => %{"operation" => "insert", "is_move_in" => true},
                 "value" => %{"id" => "3", "parent_id" => "3", "value" => "30"}
               },
               %{"headers" => %{"control" => "snapshot-end"}},
               up_to_date_ctl()
             ]} = shape_req(req, ctx.opts)
     left:  {_req, 200,
             [
               %{"headers" => %{"event" => "move-out", "patterns" => p1}},
               %{"headers" => %{"event" => "move-out", "patterns" => p1}},
               %{"headers" => %{"control" => "snapshot-end"}},
               %{
                 "headers" => %{"operation" => "insert", "is_move_in" => true},
                 "value" => %{"id" => "3", "parent_id" => "3", "value" => "30"}
               },
               %{"headers" => %{"control" => "snapshot-end"}},
               up_to_date_ctl()
             ]}
     right: {%{handle: "89020491-1765925325621538", offset: "1_4", table: "child", where: "parent_id in (SELECT id FROM parent WHERE value = 1)", live: false}, 200, [%{"headers" => %{"event" => "move-out", "patterns" => [%{"pos" => 0, "value" => "ca55a23fed822f898710b30594b40dba"}]}}, %{"headers" => %{"control" => "snapshot-end", "xip_list" => [], "xmax" => "2393", "xmin" => "2393"}}, %{"headers" => %{"event" => "move-out", "patterns" => [%{"pos" => 0, "value" => "ca55a23fed822f898710b30594b40dba"}]}}, %{"headers" => %{"is_move_in" => true, "operation" => "insert", "relation" => ["public", "child"], "tags" => ["2c592528aae5a2772434233d4b846a41"]}, "key" => "\"public\".\"child\"/\"3\"", "value" => %{"id" => "3", "parent_id" => "3", "value" => "30"}}, %{"headers" => %{"control" => "snapshot-end", "xip_list" => [], "xmax" => "2393", "xmin" => "2393"}}, %{"headers" => %{"control" => "up-to-date", "global_last_seen_lsn" => "513843840"}}]}
     stacktrace:
       .../electric/plug/router_test.exs:2779: (test)

Elixir.Electric.Shapes.ConsumerTest::test event handling handles truncate when shape has a where clause

Stack Traces | 5.01s run time

4) test event handling handles truncate when shape has a where clause (Electric.Shapes.ConsumerTest)
     .../electric/shapes/consumer_test.exs:392
     Assertion failed, no matching message after 5000ms
     The following variables were pinned:
       pid = #PID<0.9169.0>
       ref = #Reference<0.2700037891.131072001.110430>
     Showing 8 of 8 messages in the mailbox
     code: assert_receive {:DOWN, ^ref, :process, ^pid, reason} when reason in [:shutdown, shutdown: :cleanup]
     mailbox:
       pattern: {:DOWN, ^ref, :process, ^pid, reason} when reason in [:shutdown, shutdown: :cleanup]
       value:   {Support.TestStorage, :for_shape, "Electric.Shapes.ConsumerTest-shape1"}

       pattern: {:DOWN, ^ref, :process, ^pid, reason} when reason in [:shutdown, shutdown: :cleanup]
       value:   {Support.TestStorage, :get_current_position, "Electric.Shapes.ConsumerTest-shape1"}

       pattern: {:DOWN, ^ref, :process, ^pid, reason} when reason in [:shutdown, shutdown: :cleanup]
       value:   {Support.TestStorage, :snapshot_started?, "Electric.Shapes.ConsumerTest-shape1"}

       pattern: {:DOWN, ^ref, :process, ^pid, reason} when reason in [:shutdown, shutdown: :cleanup]
       value:   {Support.TestStorage, :mark_snapshot_as_started, "Electric.Shapes.ConsumerTest-shape1"}

       pattern: {:DOWN, ^ref, :process, ^pid, reason} when reason in [:shutdown, shutdown: :cleanup]
       value:   {Support.TestStorage, :set_pg_snapshot, "Electric.Shapes.ConsumerTest-shape1", %{xmin: 100, xmax: 101, xip_list: ~c"d", filter_txns?: false}}

       pattern: {:DOWN, ^ref, :process, ^pid, reason} when reason in [:shutdown, shutdown: :cleanup]
       value:   {:DOWN, #Reference<0.2700037891.131072001.110430>, :process, #PID<0.9169.0>, :noproc}

       pattern: {:DOWN, ^ref, :process, ^pid, reason} when reason in [:shutdown, shutdown: :cleanup]
       value:   {Support.TestStorage, :cleanup!, "Electric.Shapes.ConsumerTest-shape1"}

       pattern: {:DOWN, ^ref, :process, ^pid, reason} when reason in [:shutdown, shutdown: :cleanup]
       value:   {Electric.ShapeCache.ShapeCleaner, :cleanup, "Electric.Shapes.ConsumerTest-shape1"}
     stacktrace:
       .../electric/shapes/consumer_test.exs:374: anonymous fn/3 in Electric.Shapes.ConsumerTest.assert_consumer_shutdown/4
       (elixir 1.19.1) lib/enum.ex:2520: Enum."-reduce/3-lists^foldl/2-0-"/3
       .../electric/shapes/consumer_test.exs:373: Electric.Shapes.ConsumerTest.assert_consumer_shutdown/4
       .../electric/shapes/consumer_test.exs:407: (test)

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[robacourt]

LGTM. Great work!