pr-comment-build-dispatcher.yaml: Check team membership

This change is a building block for PR builds triggered by PR commands.
It checks for membership of the commenter in the Flatcar Maintainers
team.

Note that the "issue comment" event (which is also triggered on PR
comments) is only emitted to workflows in the "main" branch. So in order
to test / trigger this workflow, a transient "PR update" event is used,
and the "commenter" user's login is hard-coded for testing.

This will be updated to using the actual commenter's login before merge.

Signed-off-by: Thilo Fromm <thilofromm@microsoft.com>

.github/workflows/pr-comment-build-dispatcher.yaml

@@ -0,0 +1,57 @@
+name: "Dispatch SDK container rebuilds, OS image builds, and OS image tests from PR comments"
+on:
+  issue_comment:
+    types: [created]
+  pull_request:
+    # This is temporary for testing the workflow.
+    #  Comment events are only processed for workflows in the main branch
+    types: [opened, reopened, synchronize]
+
+permissions:
+  pull-requests: write
+
+jobs:
+
+  check_maintainer_membership:
+    # Only run if this is a PR comment that contains a valid command
+#    if: |
+#      ${{ github.event.issue.pull_request }} &&
+#        (    contains(github.event.comment.body, '/build-sdk')
+#          || contains(github.event.comment.body, '/build-image') )
+    name: Check if commenter is in the Flatcar maintainers team
+    outputs:
+      maintainers: steps.step1.output.maintainers
+    runs-on:
+      - ubuntu-latest
+    steps:
+      - name: Fetch members of the maintainers team
+        env:
+#          - requester: ${{ github.event.comment.user.login }}
+          requester: "t-lo"
+        shell: bash
+        run: |
+          curl -L --silent \
+                  -H "Accept: application/vnd.github+json" \
+                  -H "Authorization: Bearer ${{ secrets.GH_ACTIONS_ORG_READ }}" \
+                  -H "X-GitHub-Api-Version: 2022-11-28" \
+                  https://api.github.com/orgs/flatcar/teams/flatcar-maintainers/members \
+              | jq -r '.[].login' > maintainers.txt
+
+          echo "Current members of the maintainers team:"
+          cat maintainers.txt
+
+          res=false
+          echo "Checking for membership of '${{ env.requester }}'"
+          if grep -qE "^${{ env.requester }}$" maintainers.txt ; then
+            echo "Succeeded."
+            res=true
+          else
+            echo "FAILED: '${{ env.requester }} is not a member of the Flatcar maintainers team."
+          fi
+
+          $res
+
+#    name: "Build the OS image"
+#    uses: ./.github/workflows/ci.yaml
+#    with:
+#      custom_sdk_version: ${{ github.event.inputs.custom_sdk_version }}