bazel 6.4.0, rules_go v0.45, bazel-gazelle 0.35, more...

[pcj]

This is a large PR that includes:

• use bazel to 6.4.0 (was 5.4.0)
• add github actions CI. bazelci continues to run, but the default branch has not been updated in years and it is difficult to find a bazel core contrib to manage bazelci for external repos.
• migrates //external:BUILD.bazel to use the (new) yaml config file //:rules_proto_config.yaml, which works as a default config for stackb/rules_proto consumers.
• migrates //:gazelle target in this repository to use proto_gazelle, referencing the imports from other proto_repository rules.
• the javascript plugin --js_out is no longer bundled with protoc. A new dependency to protocolbuffers/protobuf-javascript added. New top-level js_core_deps.bzl macro.
• WORKSPACE re-org
• vendored google/protobuf/timestamp.proto until ts_proto can deal correctly with external repositories.
• bumped go.mod go version to 1.18
• upgraded go deps
• updated pkg/protoc/resolver.go to deal with feat(resolve): optimize applying overrides to be efficient bazel-contrib/bazel-gazelle#1687.

Upgrades:

• bazelbuild/io_bazel_rules_go upgraded from 0.39.1 to 0.44.1
• bazelbuild/bazel_gazelle upgraded from 0.31.0 to 0.35.0
• bazelbuild/rules_proto upgraded to f9b0b880d1e10e18daeeb168cef9d0f8316fdcb5 (latest)
• protocolbuffers/protobuf upgraded from 3.20.1 to v21.12. NOTE: The protobuf-javascript repo is stuck on v21 and needs to be migrated to use selected abseil imports rather than older imports that were previously vendored into protobuf repo.
• grpc/grpc upgraded from 1.54.1 to 1.54.3
• grpc-web upgraded from 1.4.2 to 1.5.0