feat: remove checkout and auth from setup-custard action

[davidcavazos]

Moves the checkout step outside of setup-custard. This gives more flexibility on what specific options to use on the code checkout.

This also embeds the JS setup code directly into the action step. This way, we don't need to checkout the tools repo for the JS source code. Eventually, all this setup code should be handled by the local runner.

The checkout on affected was not doing what we were expecting. It was checking out the caller repo, not the tools repo. So basically, the scripts file would have to exist in the language repo. Embedding the JS script is just a temporary workaround, once we have the local runner this will no longer be necessary and will go away

Additionally, this enables creating checks both on workflow_run and pull_request (not fork) so that we can test end-to-end on PRs, while not breaking PRs from forks like renovate. I made more explicit check names to disambiguate between all the "duplicated checks".