contrib/completions: sync bash completion with current CLI

[immanuwell]

bash completion drifted from the current CLI a bit.

Repro on current main:

1. Load the bash completion.
2. Try tab-completing these:
   • runc fe
   • runc run --k
   • runc run --d
   • runc delete --f
   • runc exec --t
   • runc list --format
3. You hit wrong or missing suggestions:
   • features is missing
   • --keep is missing
   • --detatch is suggested
   • --format, is suggested for delete
   • --tty, is suggested for exec
   • text is suggested for list --format, but help says table|json

This syncs the completion script with the current --help output, adds the missing entries, and adds a small regression test.

Pretty small fix, but nice QoL. easy to hit when you tab around.

[kolyshkin]

LGTM overall, although runc features is not really targeted to be used from CLI (it's for upper-level runtime to query what's available and what's not).

[kolyshkin]

@immanuwell your test cases are failing. I am also unsure if it makes sense to perform such kind of tests.

[immanuwell]

@kolyshkin I addressed all your suggestions, PTAL

[kolyshkin]

Basically, same feedback:

• not sure if runc features need to be exposed to bash-completion;
• not sure if such integration tests make sense (I mean, we're checking that some specific options are hardcoded -- will it ever help to catch a regression, or what?).

To me, a good test would be some check that if a new option is ever added, it's also mentioned in bash completion.