[27.x backport] Completion for events --filter

[thaJeztah]

• backport Completion for events --filter #5538

---

Adds completion for docker events --filter.

There are different types of filters, requiring different completion logic.
Some filters have static values, others require API lookups.
In some cases, trailing spaces of intermediate completions have to be suppressed.

The completion logic is complex because cobra does not offer support for compound flag values.
The handler for the --filter flag serves as the central entrypoint to all completions.

How to verify:
in a dev container, run make completion, then trigger completions, e.g.

$ docker events --filter <TAB><TAB>
container=  event=      label=      node=       type=       
daemon=     image=      network=    scope=      volume= 
$ docker events --filter event=c<TAB><TAB>
checkpoint  commit      connect     copy        create
$ docker events --filter image=<TAB><TAB>
docker-cli-dev:latest  docker-cli-e2e:latest  registry:2

The completions should correspond to those of the legacy bash completion.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 70.37037% with 32 lines in your changes missing coverage. Please review.

Project coverage is 58.41%. Comparing base (9128f7b) to head (8caf347).
Report is 17 commits behind head on 27.x.

Additional details and impacted files

@@            Coverage Diff             @@
##             27.x    #5614      +/-   ##
==========================================
+ Coverage   58.38%   58.41%   +0.02%     
==========================================
  Files         336      337       +1     
  Lines       28781    28899     +118     
==========================================
+ Hits        16805    16881      +76     
- Misses      11009    11050      +41     
- Partials      967      968       +1     

[thaJeztah]

OH! this needs some minor patching for this branch;

63.76 cli/command/system/cmd.go:1: : # github.com/docker/cli/cli/command/system [github.com/docker/cli/cli/command/system.test]
63.76 cli/command/system/client_test.go:22:79: undefined: container.Summary
63.76 cli/command/system/client_test.go:38:103: undefined: container.Summary
63.76 cli/command/system/client_test.go:42:21: undefined: container.Summary
63.76 cli/command/system/completion_test.go:30:86: undefined: container.Summary
63.76 cli/command/system/completion_test.go:31:25: undefined: container.Summary
63.76 cli/command/system/completion_test.go:42:86: undefined: container.Summary (typecheck)
63.76 package system

[laurazard]

It's a small nit, but I wonder if we should squash your changes adjusting the types into the original commit that introduced them – otherwise if we have to revert them or do anything we need to remember to move them both together because one won't build without the other.

WDYT @thaJeztah?

[thaJeztah]

Ah, yes, I'm good with squashing; with these I'm always leaning two ways; "is it clearer to have a separate commit showing this is what we modified" or (also for bisecting) "this is the backport (but it's modified)".

Let me squash the commits, as I think that's what we usually did.

[thaJeztah]

Squashed! ❤️

[laurazard]

Looks great, thanks!