add GitLabPatchesCustomField to display merge requests that mention a task
Uses GitLab search to find MRs which mention a task in a bug trailer in their description text, similar to what we do for Gerrit patches.
Unfortunately, due to GitLab search limitations, this doesn't work with commits.
This requires a gitlab.api_key
configuration value to be deployed. Adding that is done here:
Unanswered question: Is a project access token the right thing for that? It seems to work on testing.
Bug: T324149