add a github workflow checking for x-maintenance-intent in the opam files of the PR

.github/workflows/maintenance-intent.yml

@@ -0,0 +1,51 @@
+name: maintenance-intent present
+
+on:
+  pull_request
+
+jobs:
+  changed_files:
+    runs-on: ubuntu-latest
+    name: Check changed files for x-maintenance-intent field
+    steps:
+      - uses: actions/checkout@v4
+      - name: Get changed files
+        id: changed-files
+        uses: tj-actions/changed-files@v45
+
+      - name: Find opam files without x-maintenance-intent field
+        id: missing-intent
+        env:
+          ALL_CHANGED_FILES: ${{ steps.changed-files.outputs.all_changed_files }}
+        run: |
+          for file in ${ALL_CHANGED_FILES}; do
+            bn=$(basename ${file})
+            if [ $bn = "opam" ]; then
+              maint_int_present=$(grep "^x-maintenance-intent: " ${file} | wc -l || true)
+              if [ "$maint_int_present" -eq 0 ]; then
+                echo "- $file" >> maint-int.md
+              fi;
+            fi;
+          done;
+          if [ -f maint-int.md ]; then
+            echo "modified=true" >> $GITHUB_OUTPUT
+            echo "The following opam files lack the x-maintenance-intent field:" > maint-int2.md
+            echo "" >> maint-int2.md
+            cat maint-int.md >> maint-int2.md
+            echo "" >> maint-int2.md
+            echo "Please look at https://github.com/ocaml/opam-repository/blob/master/governance/policies/archiving.md#specification-of-the-x--fields-used-in-the-archiving-process for further information." >> maint-int2.md
+            mv maint-int2.md maint-int.md
+          else
+            echo "modified=false" >> $GITHUB_OUTPUT
+          fi
+
+      - name: Add PR Comment
+        if: steps.missing-intent.outputs.modified == 'true'
+        uses: marocchino/sticky-pull-request-comment@v2
+        with:
+          recreate: true
+          path: maint-int.md
+
+      - name: Write to Job Summary
+        if: steps.missing-intent.outputs.modified == 'true'
+        run: cat maint-int.md >> $GITHUB_STEP_SUMMARY