Add github action PR build for 5.1

.github/workflows/dispatch-pr-build.yml

@@ -0,0 +1,52 @@
+name: Request dispatched PR Build
+
+on:
+  pull_request:
+    types: [ opened, reopened, synchronize, edited ]
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  dispatchedPR:
+    name: Dispatch wait and check
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Check if PR edit changed deps string
+        if: ${{ github.event.action == 'edited' }}
+        id: pr-string-changed
+        continue-on-error: true
+        run: |
+          old_pr_string=$(grep -P '^/(jenkins-pr-deps|jpd|prd)' <<< "$OLD_PR_BODY" | \
+            grep -ioP '(Graylog2/\S+?#|https?://github.com/Graylog2/\S+?/pull/)[0-9]+' || true)
+          new_pr_string=$(grep -P '^/(jenkins-pr-deps|jpd|prd)' <<< "$NEW_PR_BODY" | \
+            grep -ioP '(Graylog2/\S+?#|https?://github.com/Graylog2/\S+?/pull/)[0-9]+' || true)
+          if [ "$old_pr_string" != "$new_pr_string" ]; then
+            echo "PR deps string change detected: \"$old_pr_string\" -> \"$new_pr_string\""
+            echo "Re-triggering PR build..."
+            exit 0
+          fi
+          exit 1
+        env:
+          OLD_PR_BODY: "${{ github.event.changes.body.from }}"
+          NEW_PR_BODY: "${{ github.event.pull_request.body }}"
+
+      - name: dispatch job to graylog-project-internal
+        if: ${{ github.event.action != 'edited' || steps.pr-string-changed.outcome == 'success' }}
+        run: >
+          gh workflow run -R Graylog2/graylog-project-internal pr-build.yml --ref master
+          -f caller_repo=${{ github.repository }}
+          -f caller_pr_nr=${{ github.event.number }}
+          -f caller_base_branch=${{ github.base_ref || github.ref_name }}
+          -f caller_head_branch=${{ github.head_ref }}
+          -f head_sha=${{ github.event.pull_request.head.sha }}
+          -f initial_actor="${{ github.actor }}/${{ github.triggering_actor }}"
+        env:
+          GITHUB_TOKEN: ${{ secrets.PAT_GRAYLOG_PROJECT_INTERNAL_WORKFLOW_RW }}
+
+      - name: Give dispatched build time to add its status
+        run: sleep 20
+        # This is mostly cosmetic. If this workflow finishes before the dispatched
+        # build creates the status on the PR, the build will show up green for a while.