Remote code improvements
# What does this PR do?

This PR adds a few improvements to the code on the Hub API, mainly:
- if `trust_remote_code` is unset, we ask the user to validate or not (with a timeout of 30s for users launchin script)
- in case of conflict between code on the Hub and local code (for when Falcon or MPT are added in Transformers for instance),  `trust_remote_code=False` will execute the local code, `trust_remote_code=True` the one on the Hub
_The documentation is not available anymore as the PR was closed or merged._