Pause and resume sessions from CLI

[m-alisafaee]

Describe the solution you'd like
We implemented session hibernation in SwissDataScienceCenter/renku-notebooks#1518 that allows users to pause and resume sessions from the UI. We should implement proper CLI commands to have the similar functionality for sessions that are managed by CLI.

renku session pause <session-name>

renku session resume/start/restart <session-name>

As nice-to-haves:

• When a user runs renku session stop on a session that has unsaved work, the cli warns them and prompts to ask if they really want to delete the session and lose unsaved changes, or if they want to pause it.
• If possible, there is no difference to the user between running renku session start and renku session resume on a paused session (so the user doesn't have to remember whether they have a paused session or are creating a new one).