Move CI from BK to GHA

Requires matrix-org/matrix-js-sdk#2307 + matrix-org/matrix-react-sdk#8372

Author: t3chguy

matrix-js-sdk/pipeline.yaml

@@ -1,22 +1,4 @@
 steps:
-  - label: ":eslint: JS Lint"
-    command:
-      - "yarn install"
-      - "yarn lint:js"
-    plugins:
-      - docker#v3.0.1:
-          image: "node:14-buster"
-          mount-buildkite-agent: false
-
-  - label: ":typescript: Types Lint"
-    command:
-      - "yarn install"
-      - "yarn lint:types"
-    plugins:
-      - docker#v3.0.1:
-          image: "node:14-buster"
-          mount-buildkite-agent: false
-
   - label: ":hammer_and_wrench: Build"
     command:
       - "yarn install"
@@ -26,29 +8,6 @@ steps:
           image: "node:14-buster"
           mount-buildkite-agent: false
 
-  - label: ":jest: Tests"
-    agents:
-      # We use a medium sized instance instead of the normal small ones because
-      # jest likes our browserified bundle so much it OOMs.
-      queue: "medium"
-    command:
-      - "yarn install"
-      - "yarn build"
-      - "yarn test"
-    plugins:
-      - docker#v3.0.1:
-          image: "node:14-buster"
-          mount-buildkite-agent: false
-
-  - label: ":page_with_curl: Docs"
-    command:
-      - "yarn install"
-      - "yarn gendoc"
-    plugins:
-      - docker#v3.0.1:
-          image: "node:14-buster"
-          mount-buildkite-agent: false
-
   - wait
 
   - label: ":horse: Trigger matrix-react-sdk"