* Refactor publish_draft_release.sh

* Switch to using arrays for storing labelled changes
* Combine changes for Polkadot and Substrate
* Change sanitised_git_logs in `lib.sh` to drop `*`s at the start
* Only look for priorities of medium or above (presence of one or more
  C1 label is enforeced by check-labels anyway, saves us some API calls)

* Ensure priorities >C1-low aren't labelled B0-silent

* Enforces presence of C-labels to designate the importance of a release
* Iterates over them on a release, takes the highest present and includes it in the release notes
* Lists the change(s) that caused the release to be that priority

* add check_tags CI job

* fix typo in gitlab-ci.yml

* add more useful CI output

* Make presence of github token optional