Add more tools to control session and file uploads

[coezbek]

The current set of tools is missing two important aspects when collaborating with an agent on a colab notebook:

1. Ability to stop the runtime and start it with a given runtime-type (GPU/CPU) again. This would be helpful in particular when letting the agent work autonomously for longer time to conserve Colab resources.
2. Upload/download files to the session.

Of course there are workarounds for point 2 by using Google Drive on both sides, but this requires giving the agent access to Google Drive which might not be desirable.