Port detection of stalled issues/MRs to GitLab
Closes #17851 (moved)
A trial run created #17853 (closed) and #17854 (closed), which illustrate what this automation produces, i.e. essentially the same as what we had in Redmine, except:
- Summary issues are created, and relevant users
@mention
'ed, instead of sending email. - Until we've figured out how to use GitLab CI, I'll run this command manually every 2 months (previously this was a cronjob running every 2 months + manual update of the config almost every time).