[18.0][IMP] analysis cronjob v19 + improvements

[hbrunn]

this needs to go into the v18 branch because cronjobs only run on the default branch.

While being at it, I added the possibility to run this manually and to not flag the base module as changed when only the upgrade_general_log.txt file has changed.

It's fine to merge this now, but the v19 analysis will only work when:

• [19.0][MIG] upgrade_analysis server-tools#3395 is merged
• Add branch 19.0 on all repos (no defaults) repo-maintainer-conf#113 is merged and a yet to be created PR has added the empty openupgrade_scripts module

[OCA-git-bot]

This PR has the approved label and has been created more than 5 days ago. It should therefore be ready to merge by a maintainer (or a PSC member if the concerned addon has no declared maintainer). 🤖