Implement volumes force detach

[r4victor]

Closes #2218

The PR:

• Refactors job termination logic. Before, process_terminating_job could be called from process_terminating_run (e.g. for non-running provisioned jobs) (evidently to safe a processing iteration). Now, process_terminating_run only marks jobs as TERMINATION, and only process_termination_jobs background task performs the jobs termination. This simplifies locking management significantly and overall logic.
• Fixes a locking bug when an instance volumes may not be detached on job termination.
• Adds backend method to check volume attach status.
• Adds job terminating logic that keeps checking volume attach status and force detaches volumes if they are stuck.
• Adds stop_duration to run configuration/profile to control max duration a job waits until force terminating.
• Fixes *_duration parameters parsing. E.g. "off" was handled for max_duration but not off and vice versa for idle_duration. true was allowed but parsed as 1.
• Other small fixes.

Next:

• Fix dstack stop CLI command to wait until the run enters the terminal status. Currently, the API is async meaning that run may be terminating for some time after the API returns.
• Handle attaching/detaching volumes for gpu blocks.