[CI] Add check for draft PRs (#5800)

* Add check for draft PRs

* Add necessary gitlab-ci boilerplate

* fix github API url (oops!)

* Add github action to retrigger pipeline

* fix workflow trigger

* rename trigger job

Co-authored-by: Benjamin Kampmann <ben@parity.io>

substrate/.maintain/gitlab/skip_if_draft.sh

@@ -0,0 +1,14 @@
+#!/bin/sh
+url="https://api.github.com/repos/paritytech/substrate/pulls/${CI_COMMIT_REF_NAME}"
+echo "[+] API URL: $url"
+
+draft_state=$(curl "$url" | jq -r .draft)
+echo "[+] Draft state: $draft_state"
+
+if [ "$draft_state" = 'true' ]; then
+  echo "[!] PR is currently a draft, stopping pipeline"
+  exit 1
+else
+  echo "[+] PR is not a draft. Proceeding with CI pipeline"
+  exit 0
+fi