Add the possibility to let the action rebase the PR for you

There are some cases where the following happens:
1. You create a PR, action-manifest-pr creates the manifest PR
2. The PR is merged. The action updates the PR.
3. A conflict occurs in the manifest-PR.

This commit adds the possibility to add a comment
to your PR that will automatically rebase the manifest-PR.
This should work even if the PR is closed.

Signed-off-by: Rubin Gerritsen <rubin.gerritsen@nordicsemi.no>

Author: rugeGerritsen

action.yml

@@ -15,6 +15,10 @@ inputs:
       required: false
       type: string
       default: manifest-pr-skip
+    rebase-comment-string:
+      required: false
+      type: string
+      default: 'action-manifest-pr please rebase'
     manifest-pr-title-details:
       required: false
       type: string
@@ -166,3 +170,15 @@ runs:
           set -e
           if (( $has_conflict == 1)) ; then git rebase upstream/main -X theirs ; fi
           git push origin auto-manifest-${{ github.event.repository.name }}-${{ github.event.pull_request.number }}:auto-manifest-${{ github.event.repository.name }}-${{ github.event.pull_request.number }} -f
+
+    - name: Rebase manifest-PR on comment
+      if: ${{ github.event.issue.pull_request }} &&
+          ${{ github.event.issue_comment.created }}
+          contains(github.event.issue_comment.created.comment, inputs.rebase-comment-string)
+      shell: bash
+      run: |
+          git checkout auto-manifest-${{ github.event.repository.name }}-${{ github.event.pull_request.number }}
+          git remote add upstream https://github.com/${{ inputs.target-repo }}
+          git fetch upstream
+          git rebase upstream/main -X theirs
+          git push origin auto-manifest-${{ github.event.repository.name }}-${{ github.event.pull_request.number }}:auto-manifest-${{ github.event.repository.name }}-${{ github.event.pull_request.number }} -f