[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/.gitlab-ci.yml

@@ -328,13 +328,3 @@ deploy-polkasync-kusama:
     POLKADOT_CI_COMMIT_REF:        "${CI_COMMIT_REF}"
   allow_failure:                   true
   trigger:                         "parity/infrastructure/parity-testnet"
-
-#### stage:                        .post
-
-check-labels:
-  stage:                           .post
-  image:                           paritytech/tools:latest
-  <<:                              *rules-pr-only
-  <<:                              *kubernetes-env
-  script:
-    - ./scripts/gitlab/check_labels.sh