ci: PLT-478: Replace FM with actions-hub call (#154)

.github/workflows/follow-merge-sync-pr.yml

@@ -0,0 +1,73 @@
+name: 'Follow Merge: Sync PR LSE'
+
+on:
+  pull_request_target:
+    types:
+      - opened
+      - closed
+      - converted_to_draft
+      - ready_for_review
+      - synchronize
+    branches:
+      - master
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.head_ref }}
+
+env:
+  DOWNSTREAM_REPOSITORY: "label-studio-enterprise"
+
+jobs:
+  sync:
+    name: "Sync"
+    if: startsWith(github.head_ref, 'fb-')
+    runs-on: ubuntu-latest
+    steps:
+      - uses: hmarr/debug-action@v3.0.0
+
+      - name: Check user's membership
+        uses: actions/github-script@v7
+        id: check-membership
+        with:
+          github-token: ${{ secrets.GIT_PAT }}
+          script: |
+            const { repo, owner } = context.repo;
+            try {
+              return (await github.rest.orgs.getMembershipForUser({
+                org: owner,
+                username: '${{ github.actor }}',
+              }))?.data?.state == "active";
+            } catch (error) {
+              return false;
+            }
+
+      - name: Notify user on failure
+        if: steps.check-membership.outputs.result == 'false'
+        uses: actions/github-script@v7
+        with:
+          github-token: ${{ secrets.GIT_PAT }}
+          script: |
+            const { repo, owner } = context.repo;
+            const result = await github.rest.issues.createComment({
+              owner,
+              repo,
+              issue_number: '${{ github.event.number }}',
+              body: [
+                'Hi @${{ github.actor }}!',
+                '',
+                `Unfortunately you don't have membership in ${owner} organization, your PR wasn't synced with ${owner}/${{ env.DOWNSTREAM_REPOSITORY }}.`
+              ].join('\n')
+            });
+
+      - name: Checkout Actions Hub
+        uses: actions/checkout@v4
+        with:
+          token: ${{ secrets.GIT_PAT }}
+          repository: HumanSignal/actions-hub
+          path: ./.github/actions-hub
+
+      - name: Dispatch Follow Merge Event
+        uses: ./.github/actions-hub/actions/follow-merge-dispatch
+        with:
+          github_token: ${{ secrets.GIT_PAT }}
+          downstream_repository: "${{ env.DOWNSTREAM_REPOSITORY }}"