Alpha release workflows: produce 4.2.x releases off of main

and 4.1.x ones off of v4.1.x, which is getting closer
to the RC stage.

Author: michaelklishin

.github/workflows/release-4.1.x-alphas.yaml

@@ -3,8 +3,7 @@ on:
   workflow_dispatch:
   push:
     branches:
-      # 4.1.x
-      - "main"
+      - "v4.1.x"
     paths:
       - "deps/*/src/**"
       - 'deps/rabbitmq_management/priv/**'

.github/workflows/release-4.2.x-alphas.yaml

@@ -0,0 +1,36 @@
+name: "Trigger a 4.2.x alpha release build"
+on:
+  workflow_dispatch:
+  push:
+    branches:
+      # 4.2.x
+      - "main"
+    paths:
+      - "deps/*/src/**"
+      - 'deps/rabbitmq_management/priv/**'
+      - ".github/workflows/**"
+      - "rabbitmq-components.mk"
+env:
+  DEV_WORKFLOW_REPOSITORY: "rabbitmq/server-packages"
+jobs:
+  trigger_alpha_build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Compute prerelease identifier from commit SHA
+        run: echo "PRERELEASE_IDENTIFIER=`echo ${{ github.sha }} | cut -c1-8`" >> $GITHUB_ENV
+      - name: Trigger a 4.0.x alpha build in ${{ env.DEV_WORKFLOW_REPOSITORY }}
+        uses: peter-evans/repository-dispatch@v3
+        with:
+          token: ${{ secrets.RABBITMQCI_BOT_TOKEN }}
+          repository: ${{ env.DEV_WORKFLOW_REPOSITORY }}
+          event-type: "new_4.2.x_alpha"
+          client-payload: |-
+            {
+              "release_repository": "${{ env.DEV_WORKFLOW_REPOSITORY }}",
+              "release_description": "Commit: https://github.com/rabbitmq/rabbitmq-server/commit/${{ github.sha }}, pushed at: ${{ github.event.repository.pushed_at }}",
+              "prerelease": true,
+              "prerelease_kind": "alpha",
+              "prerelease_identifier": "${{ env.PRERELEASE_IDENTIFIER }}",
+              "release_title": "RabbitMQ ${{ vars.SERVER_42_NEXT_PATCH_VERSION }}-alpha.${{ env.PRERELEASE_IDENTIFIER }} (from ${{ github.event.repository.pushed_at }})",
+              "base_version": "${{ vars.SERVER_42_NEXT_PATCH_VERSION }}"
+            }