[CI] Move check_labels to github actions (#8099)

* move lib.sh to common dir

* make check-labels a github action workflow

substrate/.maintain/github/check_labels.sh

@@ -0,0 +1,49 @@
+#!/usr/bin/env bash
+
+#shellcheck source=../common/lib.sh
+source "$( cd "$( dirname "${BASH_SOURCE[0]}" )" >/dev/null 2>&1 && pwd )/../common/lib.sh"
+
+repo="$GITHUB_REPOSITORY"
+pr="$GITHUB_PR"
+
+ensure_labels() {
+  for label in "$@"; do
+    if has_label "$repo" "$pr" "$label"; then
+      return 0
+    fi
+  done
+  return 1
+}
+
+# Must have one of the following labels
+releasenotes_labels=(
+  'B0-silent'
+  'B3-apinoteworthy'
+  'B5-clientnoteworthy'
+  'B7-runtimenoteworthy'
+)
+
+criticality_labels=(
+  'C1-low'
+  'C3-medium'
+  'C7-high'
+  'C9-critical'
+)
+
+echo "[+] Checking release notes (B) labels"
+if ensure_labels "${releasenotes_labels[@]}";  then
+  echo "[+] Release notes label detected. All is well."
+else
+  echo "[!] Release notes label not detected. Please add one of: ${releasenotes_labels[*]}"
+  exit 1
+fi
+
+echo "[+] Checking release criticality (C) labels"
+if ensure_labels "${criticality_labels[@]}";  then
+  echo "[+] Release criticality label detected. All is well."
+else
+  echo "[!] Release criticality label not detected. Please add one of: ${criticality_labels[*]}"
+  exit 1
+fi
+
+exit 0