[18.0][IMP] add a github workflow that generates test databases used in CI

[hbrunn]

In #5370 I claimed that #5355 not failing in CI is because the test databases don't include translations, but that's wrong. Anyways, I spent the morning writing this workflow to have tests databases regenerated regularly, that's a good thing to have in its own right, as there are relevant changes from time to time which might break existing scripts.

You can inspect the results in https://github.com/hbrunn/OpenUpgrade/releases/tag/databases

• update https://github.com/OCA/OpenUpgrade/blob/documentation/docsource/100_maintain_repository.rst to point to this workflow instead of a non-existing wiki page

Fixes #5370

[legalsylvain]

update https://github.com/OCA/OpenUpgrade/blob/documentation/docsource/100_maintain_repository.rst to point to this workflow instead of a non-existing wiki page

My bad. It looks like I have destroyed this page, without having updated the new documentation :

https://github.com/OCA/OpenUpgrade/wiki/_compare/d88c28abd294626b684fc6360561218c173d1287

[legalsylvain]

Some remarks inline.

Otherwise, very great improvment ! thanks !