Adding PR gatekeeper (#4869)

Signed-off-by: Danny Kopping <danny.kopping@grafana.com>

.github/approve_config.yml

@@ -0,0 +1,18 @@
+approvals:
+  minimum: 1
+  groups:
+    maintainers:
+      minimum: 1
+      from:
+        users:
+          - adityacs
+          - cyriltovena
+          - dannykopping
+          - davkal
+          - slim-bean
+          - gouthamve
+          - joe-elliott
+          - owen-d
+          - sandeepsukhani
+          - sh0rez
+          - tomwilkie

.github/workflows/pr-gatekeeper.yml

@@ -0,0 +1,28 @@
+name: 'PR Gatekeeper'
+
+on:
+  pull_request:
+    types:
+      [
+          assigned,
+          unassigned,
+          opened,
+          reopened,
+          synchronize,
+          review_requested,
+          review_request_removed
+      ]
+  pull_request_review:
+
+jobs:
+  pr-gatekeeper:
+    name: Maintainer Approval Check
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+        continue-on-error: false
+      - uses: octodemo/pr-gatekeeper@v1.0.0
+        with:
+          token: ${{ secrets.GH_BOT_ACCESS_TOKEN }}
+          config-file: ./.github/approve_config.yml