[CI] Move check_labels to github actions (#2415)

* move lib.sh to common dir

* make check-labels a github action

* check out the repo

* fix secrets

* add labelled PR type

* remove check-labels job from gitlab

* trigger on unlabelling also

polkadot/scripts/github/check_labels.sh

@@ -0,0 +1,56 @@
+#!/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'
+  'B1-releasenotes'
+  'B7-runtimenoteworthy'
+)
+
+priority_labels=(
+  'C1-low'
+  'C3-medium'
+  'C7-high'
+  'C9-critical'
+)
+
+echo "[+] Checking release notes (B) labels for $CI_COMMIT_BRANCH"
+if ensure_labels "${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 priority (C) labels for $CI_COMMIT_BRANCH"
+if ensure_labels "${priority_labels[@]}";  then
+  echo "[+] Release priority label detected. All is well."
+else
+  echo "[!] Release priority label not detected. Please add one of: ${priority_labels[*]}"
+  exit 1
+fi
+
+# If the priority is anything other than C1-low, we *must not* have a B0-silent
+# label
+if has_label "$repo" "$CI_COMMIT_BRANCH" 'B0-silent' &&
+  ! has_label "$repo" "$CI_COMMIT_BRANCH" 'C1-low' ; then
+  echo "[!] Changes with a priority higher than C1-low *MUST* have a B- label that is not B0-Silent"
+  exit 1
+fi
+
+exit 0