feat: make safety independant of tox

Hello,

This one might need a bit of discussion first, it changes safety from needing an entry in tox to be more general.

This has the advantage of being able to add it directly to ALL projects at once which is great... but this won't work if the project has a requirements(-frozen).txt of something like that ... but we don't do that yet.

I guess we can have several safety versions and apply the good one depending of the context, but for now this should work in 95% of the situations (and for all cubes and generic project, but not for a few client projects) which will be better than currently.

Some project do have a "safety" entry in their tox file already.

Another solution would be a new code-doctor rule to update the tox file which will then be customized after that but it's much more work.

Here is an example of this template running: https://forge.extranet.logilab.fr/logilab/cubes/crm/-/jobs/601046