cli/container: use github.com/moby/sys/capability for completions

[thaJeztah]

• relates to f30158d / various improvements to shell completions #5238

We used a hard-coded list of capabilities that we copied from containerd, but the new "capability" package allows use to have a maintained list of capabilities.

There's likely still some improvements to be made;

First of all, the capability package could provide a function to get the list of strings.

On the completion-side, we need to consider what format is most convenient; currently we use the canonical name (uppercase and "CAP_" prefix), however, tab-completion is case-sensitive by default, so requires the user to type uppercase letters to filter the list of options.

Bash completion provides a completion-ignore-case on option to make completion case-insensitive (https://askubuntu.com/a/87066), but it looks to be a global option; the current cobra.CompletionOptions also don't provide this as an option to be used in the generated completion-script.

Fish completion has smartcase (by default?) which matches any case if all of the input is lowercase.

Zsh does not have a dedicated option, but allows setting matching-rules (see https://superuser.com/a/1092328).

- What I did

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[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 60.07%. Comparing base (f4fab2c) to head (462e082).
Report is 70 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5480      +/-   ##
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+ Coverage   60.05%   60.07%   +0.02%     
==========================================
  Files         345      345              
  Lines       23440    23447       +7     
==========================================
+ Hits        14076    14085       +9     
+ Misses       8390     8388       -2     
  Partials      974      974              

[thaJeztah]

@laurazard updated; I added a minimal unit-test. Perhaps wouldn't hurt to add tests for some of the other ones as well (but didn't want to stuff those in this PR).

For the "case-insensitive" auto-complete, I also want to do some experimenting in follow-ups. Related to that, I opened a PR to normalize and de-duplicate values in the client before we send the request;

• client: ContainerCreate: normalize CapAdd, CapDrop capabilities moby/moby#48551

[laurazard]

Thanks! LGTM