Use released docs package from renovate to generate docs

[viceice]

What would you like to be able to do?

We should use the now released precompiled renovate docs asset instead of the git submodule.
This will speedup docs generation.
Dowside: we need a renovate release to update docs.

Did you already have any implementation ideas?

• remove submodule
• add renovate version to a file and let renovate selfupdate
• download file in get-docs
• optional allow setting an env to use local docs from renovate repo outside of this repo for debugging

[HonkingGoose]

Dowside: we need a renovate release to update docs.

Don't we already need a Renovate release to publish our docs? Or did the docs site get updated regularly on a cron timer as well?

[viceice]

Currently this repo has the renovate repo as git submodule. So this repo get's updated shortly after a commit on main on renovate repo.
And the update will trigger a docs publish.

[HonkingGoose]

We should also update the README.md and the contributing.md files, so they explain how to use the released docs package. That way I know how to preview the docs. 😄