feat: add workflow to merge release branch (#256)

Re-usable workflow to be used as a post-release step.

.github/workflows/merge-release-branch.yml

@@ -0,0 +1,74 @@
+
+name: Merge release branch into main
+
+on:
+  workflow_call:
+    inputs:
+      version:
+        type: string
+        description: The release branch version to merge into main
+        required: true
+      repo:
+        type: string
+        description: The repository to create the PR (org/repo format)
+        required: true
+
+  workflow_dispatch:
+    inputs:
+      version:
+        type: string
+        description: The release branch version to merge into main
+        required: true
+      repo:
+        type: string
+        description: The repository to create the PR (org/repo format)
+        required: true
+
+defaults:
+  run:
+    shell: bash
+
+jobs:
+  merge-release-branch:
+    name: Submit PR to merge release branch into main
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout ${{ inputs.repo }}
+        uses: actions/checkout@v4
+        with:
+          repository: ${{ inputs.repo }}
+          ref: release/${{ inputs.version }}
+          submodules: true
+          token: ${{ secrets.BOT_TOKEN_WORKFLOW }}
+
+      - name: Create PR
+        id: cpr
+        uses: peter-evans/create-pull-request@v7
+        with:
+          token: ${{ secrets.BOT_TOKEN_WORKFLOW }}
+          commit-message: "chore: merge release/${{ inputs.version }} into main"
+          committer: eclipse-zenoh-bot <[email protected]>
+          author: eclipse-zenoh-bot <[email protected]>
+          base: main
+          branch: release/${{ inputs.version }} 
+          delete-branch: false
+          title: 'chore: Merge release/${{ inputs.version }} into main'
+          body: |
+              - Merge release/${{ inputs.version }} into main
+              - Open new development line
+          labels: internal
+
+      - name: Enable auto merge for the pull request
+        if: ${{ steps.cpr.outputs.pull-request-operation == 'created' }}
+        run: >
+          gh pr merge "${{ steps.cpr.outputs.pull-request-number }}"
+          --subject "chore: Merge release/${{ inputs.version }} into main (#${{ steps.cpr.outputs.pull-request-number }})"
+          --repo "${{ inputs.repo }}"
+          --auto
+        env:
+          GH_TOKEN: ${{ secrets.BOT_TOKEN_WORKFLOW }}
+
+      - name: Add the PR as annotation to workflow run
+        if: ${{ steps.cpr.outputs.pull-request-operation == 'created' }}
+        run: >
+          echo "::notice:: Created PR: https://github.com/${{ inputs.repo }}/pull/${{ steps.cpr.outputs.pull-request-number }}"