Add test settings file for proxito

[stsewd]

This is needed to allow us to run tests with the proxito settings in
.com (and probably in .org too)

[humitos]

I think this makes sense.

We should double check that this won't break production. I don't remember exactly how is the proxito settings file generated, but I think it's based on readthedocs/settings/proxito.py which is deleted in this PR.

[stsewd]

@humitos looks like we are not using any file from here for the production settings, neither on .org or .com. We should use the base settings from here after it's merged so we don't duplicate them.

[ericholscher]

We should merge this after fixing the conflict.

[davidfischer]

After this was merged, in my local environment it seems to create an empty readthedocs/settings/proxito.py. I think it's the result of this. This causes proxito to fail to start due to the SECRET_KEY not being set.

Edit: to be clear, the empty file is created while running inv docker.up.

[humitos]

Yes. This breaks the local environment. I think it's better to have everything related to tests inside the tests/ directory, so they are isolated. I propose to move this to readthedocs/proxito/tests/settings.

[humitos]

I open a PR with a fix for this at #6703 without changing the structure.