Utilize GitHub Actions to check for SEMVER impact label (#2470)

It is easy to forget to label PRs with their SEMVER impact when
merging.

Adding a workflow to automate labelling will help prevent
users from missing labels when merging.

Let's check the PR body description for user selected impact,
and automatically add the label to the PR when merging.

This approach allows the user to not even have to add the label
themselves.

.github/workflows/pr-merge.yml

@@ -0,0 +1,69 @@
+name: Pull Request Review Action
+on:
+    pull_request_target:
+        types:
+          - closed
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
+  cancel-in-progress: true
+
+jobs:
+    check-pr-label:
+        if: ${{ github.event.pull_request.merged }}
+        runs-on: ubuntu-latest
+        steps:
+          - uses: actions/checkout@v3
+          - name: Check for PR description label
+            id: check_pr_description_label
+            run: |
+              python scripts/process_message.py "${TEXT_BODY}" > processed_body.txt
+              processed_body=$(cat processed_body.txt)
+              proposed_version_impact=$(echo "$processed_body" | awk '/Major \\\(when you make incompatible API changes\\\)/,/Patch \\\(when you make backward compatible bug fixes\\\)/')
+              is_major=$(echo "$proposed_version_impact" | grep -qi '\[X\] Major'; echo $((1-$?)))
+              is_minor=$(echo "$proposed_version_impact" | grep -qi '\[X\] Minor'; echo $((1-$?)))
+              is_patch=$(echo "$proposed_version_impact" | grep -qi '\[X\] Patch'; echo $((1-$?)))
+              num_labels_chosen=$(($is_major + $is_minor + $is_patch))
+              echo "num_labels_chosen=$num_labels_chosen" >> $GITHUB_OUTPUT
+              if [[ "$num_labels_chosen" -eq 0 ]]; then
+                echo "message=$(echo "@${MERGE_AUTHOR} Each PR must have a SEMVER impact label, please remember to label the PR properly.")" >> $GITHUB_OUTPUT
+              elif [[ "$num_labels_chosen" -ge 2 ]]; then
+                echo "message=$(echo "@${MERGE_AUTHOR} Each PR can only have one SEMVER impact label, please remember to label the PR properly.")" >> $GITHUB_OUTPUT
+              else
+                echo "message=$(echo "SEMVER impact selected.")" >> $GITHUB_OUTPUT
+                echo "chosen_label=$(
+                    if [ "$is_major" -eq 1 ]; then
+                        echo "r.Major"
+                    elif [ "$is_minor" -eq 1 ]; then
+                        echo "r.Minor"
+                    elif [ "$is_patch" -eq 1 ]; then
+                        echo "r.Patch"
+                    fi
+                 )" >> $GITHUB_OUTPUT
+              fi
+            env:
+              TEXT_BODY: ${{ github.event.pull_request.body }}
+              MERGE_AUTHOR: ${{ github.event.sender.login }}
+          - name: Assign label based on version impact
+            uses: actions/github-script@v7
+            with:
+                script: |
+                    if (process.env.NUM_LABELS_CHOSEN != 1) {
+                      github.rest.issues.createComment({
+                        issue_number: context.payload.pull_request.number,
+                        owner: context.repo.owner,
+                        repo: context.repo.repo,
+                        body: process.env.MESSAGE,
+                      });
+                    } else {
+                        github.rest.issues.addLabels({
+                            issue_number: context.payload.pull_request.number,
+                            owner: context.repo.owner,
+                            repo: context.repo.repo,
+                            labels: [process.env.CHOSEN_LABEL]
+                        });
+                    }
+            env:
+                NUM_LABELS_CHOSEN: ${{ steps.check_pr_description_label.outputs.num_labels_chosen }}
+                MESSAGE: ${{ steps.check_pr_description_label.outputs.message }}
+                CHOSEN_LABEL: ${{ steps.check_pr_description_label.outputs.chosen_label }}