Adds 'handbook' to the list of GitLab projects that require maintainer access
This MR updates the tw_onboarding template - it adds the handbook
project to the list of GitLab projects that require maintainer access.
For context: https://gitlab.slack.com/archives/CDWGE0DDY/p1695722141285309?thread_ts=1695721135.474519&cid=CDWGE0DDY.
Edited by Lysanne Pinto