Feature request: bash completion script

Is your feature request related to a problem? Please describe.
I'm frustrated—especially in a recovery environment where I don't have the ability to use multiple terminal windows/tabs, etc.,—that there's no tab/bash completion for timeshift.

Describe the solution you'd like
CLI users are familiar with how tab completion works... Given what e.g., apt completion can do, tab completion can be quite sophisticated so all of the --flags should be tab-completable, the snapshot names should be tab-completeable.

At a minimum, being able to autocomplete the snapshot names (which can be had from something like $ timeshift --list|tail -n 7|awk '{print $3}') and the --flags would be a major improvement.

Maybe --targets, --snapshot-device and --grub-device too? (I haven't used them so not sure how realistic/useful that would be.)

Describe alternatives you've considered
Manually typing everything into the CLI. PR #504.

Additional context
Add any other context or screenshots about the feature request here.

Start by reviewing the timeshift CLI behavior, especially timeshift --list and the documented --flags, snapshot names, --targets, --snapshot-device, and --grub-device options. Check the referenced PR #504 for existing work. Done means Bash completion provides useful suggestions for the flags and snapshot names, with any additional options validated for usefulness.