chore: minor improvement to docs generation

[IronCore864]

Minor fix to the automated doc generation.

Changes:

• When getting command help output, use go run ./cmd/pebble.
• GitHub Actions job to check if the automated CLI reference docs have been changed.
• Regenerate CLI command reference doc to fix stty cols 80 issue.

[benhoyt]

Thanks for this. Couple of comments. I also don't fully understand why the columns thing is now fixed.

[IronCore864]

Add some notes for the issue of the column in case we need to reinvestigate it in the future:

• My env is multipass.
• After abundant testing, stty cols works steadily if no terminal-resizing is done during the period the script is running. The behaviour is consistent regardless of the terminal width.
• Broken output can be reproduced steadily if the terminal width is resized while the script runs.

[IronCore864]

Upgraded to python 3.12 and the latest version of tox (4.17). Triggered the CI test and it passed: https://github.com/canonical/pebble/actions/runs/10313091679/job/28549325132?pr=477.