Make it possible to change retro creation dates.

Currently we seem to rely on GitLab pipeline schedules.

It seems like @plafoucriere would like to adjust the issue creation date to right after kickoff.

Could we change the design of the app somehow, so that it:

1. Runs daily
2. A group can specify a open date / close date
3. In the dates between it updates the issue description if necessary

/cc @gonzoyumo