Implements smart merge v2 (yarnpkg#4177)

.github/workflows/pr-smart-merge-apply.yml

@@ -0,0 +1,68 @@
+on:
+  workflow_run:
+    workflows: ['Smart merge: Generate']
+    types:
+      - completed
+
+name: 'Smart merge: Apply'
+jobs:
+  apply:
+    name: 'Apply the update changeset'
+    runs-on: ubuntu-latest
+    if: |
+      github.event.workflow_run.event == 'pull_request' &&
+      github.event.workflow_run.conclusion == 'success'
+
+    steps:
+      - uses: actions/checkout@v3
+        with:
+          ref: ${{github.event.workflow_run.head_sha}}
+
+      - name: 'Download the artifacts'
+        uses: actions/github-script@v3
+        with:
+          script: |
+            const fs = require(`fs`);
+
+            const artifacts = await github.actions.listWorkflowRunArtifacts({
+               owner: context.repo.owner,
+               repo: context.repo.repo,
+               run_id: ${{github.event.workflow_run.id}},
+            });
+
+            const matchArtifact = artifacts.data.artifacts.filter(artifact => {
+              return artifact.name == `pr`;
+            })[0];
+
+            const download = await github.actions.downloadArtifact({
+               owner: context.repo.owner,
+               repo: context.repo.repo,
+               artifact_id: matchArtifact.id,
+               archive_format: `zip`,
+            });
+
+            fs.writeFileSync(`${{github.workspace}}/pr.zip`, Buffer.from(download.data));
+
+      - name: Unpack the artifacts
+        run: unzip pr.zip
+
+      - name: Apply the changeset
+        run: |
+          PR_META=$(curl https://api.github.com/repos/yarnpkg/berry/pulls/'${{github.event.inputs.pr}}')
+
+          PR_REPO=$(jq -r .head.repo.full_name <<< "$PR_META")
+          PR_REF=$(jq -r .head.ref <<< "$PR_META")
+
+          git config user.name "Yarn Bot"
+          git config user.email [email protected]
+
+          git remote add pr-source https://'${{secrets.YARNBOT_TOKEN}}'@github.com/"$PR_REPO".git
+
+          git fetch --depth=1 pr-source "$PR_REF":local
+          git checkout local
+
+          git merge --no-commit origin/master || true
+          git apply pr/update.patch
+          git commit -m 'Auto-merge with master'
+
+          git push pr-source local:"$PR_REF"

.github/workflows/pr-smart-merge-reset.yml

@@ -0,0 +1,23 @@
+on:
+  pull_request_target:
+    types: [labeled]
+
+name: 'Smart merge: Reset'
+jobs:
+  generate:
+    name: 'Remove the label'
+    runs-on: ubuntu-latest
+    if: |
+      github.event.label.name == 'infra: pending update'
+
+    steps:
+      - name: 'Remove the label'
+        uses: actions/github-script@v3
+        with:
+          script: |
+            await github.rest.issues.removeLabel({
+               owner: context.repo.owner,
+               repo: context.repo.repo,
+               issue_number: context.pull_request.number,
+               name: `infra: pending update`,
+            });