Add termination reason and message to the runner API

[r4victor]

Closes #2202
Closes #1701

This PR:

• Adds termination_reason and termination_message to the runner API.
• Returns "Max duration exceeded" in termination_message when job is terminated due to max duration.
• Adds max_duration_exceeded termination reason but does not use it yet for backward compatibility with old clients.
• Makes shim/runner return lowercase termination reasons (termination reason values) for consistency with the server API.

The CLI error when max duration exceeded:

Installing extension 'ms-toolsai.jupyter'...
Run failed with error code CONTAINER_EXITED_WITH_ERROR.
Error: Max duration exceeded
Check CLI, server, and run logs for more details.

[r4victor]

I was also trying to switch to enum for termination reason in shim but it don't think it's feasible. The shim can accept a termination reason from the server and enumerating possible values set by the server will make backward compatibility challenging.

[un-def]

Also here:

dstack/src/dstack/_internal/server/services/jobs/__init__.py

Line 309 in 80e9fae

reason = job_model.termination_reason.name

.name → .value for a lowercase literal