Add --no-session-cache flag

[reynoldsnlp]

Describe the feature or problem you'd like to solve

Add a flag that blocks caching the session (to avoid cluttering up session list in copilot --resume)

Proposed solution

Put session caching behind a flag (default TRUE) which can be overridden by the argument --no-session-cache so that the user can manually block caching for a session that is expected to be disposable. This would be especially helpful for use together with copilot --no-session-cache --prompt ... since prompt calls are virtually never going to require --resumeing.

Example prompts or workflows

$ copilot --no-session-cache --prompt "..."
# The prompt session is not cached
$ copilot --resume
# The list of cached sessions does NOT contain the `--prompt` call above.

### Additional context

_No response_