Add CI to the Adaptive repository for reaxt-rxjs

[rveciana]

I think that activation the current CI would work directly, as it's not deploying anything and only needs a secret, bundlewatch-github-token, that doesn't seem to affect the original repo and could be created for us too.

Other tactics, as conditional execution depending on the repo, will need the approval from the original repo owners, and I think it would be better if we can avoid it.