Run Examples on GPU for Documentation

[simone-silvestri]

This PR is just a test to check that the documentation build triggers correctly on the GPU on the Caltech cluster and the results are literated correctly.

The setup now is that the documentation build without examples runs through github actions every commit while the documentation with examples runs every commit when the label Generate docs is attached (and stops running if we remove the label) and (should) run every time the PR is merged.

thanks @Sbozzolo for helping with the setup