Add CI check for loader changes

Changes in the loader code require a restart of PostgreSQL during
upgrades. This check creates awareness of these changes and allows the
coordination of the update process early.

.github/workflows/loader-check.yaml

@@ -0,0 +1,38 @@
+name: Check for loader changes
+"on":
+  pull_request:
+    types: [opened, synchronize, reopened, edited]
+jobs:
+  check_changelog_file:
+    name: Check for loader changes
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout source
+        uses: actions/checkout@v3
+
+      - name: Check if the pull request changes the loader
+        shell: bash --norc --noprofile {0}
+        env:
+          GH_TOKEN: ${{ github.token }}
+          BODY: ${{ github.event.pull_request.body }}
+          PR_NUMBER: ${{ github.event.pull_request.number }}
+        run: |
+          # Get the list of modified files in this pull request
+          files=$(gh pr view $PR_NUMBER --json files --jq '.files.[].path')
+
+          # Ignore loader changes if acknowledged
+          if echo "$BODY" | egrep -qsi "Acknowledge-check:[[:space:]]*loader-change"; then
+            exit 0
+          fi 
+
+          # Check for loader changes
+          if echo "${files}" | grep -Eq "^src/loader/.+$"; then
+            echo "Warning: This PR does change the loader. Therefore, upgrading to the next TimescaleDB"
+            echo "version requires a restart of PostgreSQL. Please coordinate the release with the"
+            echo "cloud team before merging."
+            echo 
+            echo "After the release is coordinated, add:"
+            echo "Acknowledge-check: loader-change"
+            echo "to the PR message to acknowledge this warning"
+            exit 1
+          fi