feat(zsh): add context argument completion

[acouvreur]

- What I did
Add a -c --context docker option completion, resolves -c and --context with the description "Execute the command in a docker context".
And resolves available contexts docker -c=<tab>

It also adds the context to the docker_options so the completion is depending on the given context.

- How I did it
This use the same function to list contexts previously added and use of docker_options variable

- How to verify it
Type docker --<tab> should add a --context option
Then type docker --context <tab> should give you the list of contexts available

Have a distant context and try to inspect a resource on it docker -c my-context inspect <TAB> should list you the resources of the given context.
- Description for the changelog
add docker --context argument completion

- A picture of a cute animal (not mandatory but encouraged)

[codecov-commenter]

Codecov Report

Merging #3130 (79638e6) into master (2ebf5d9) will increase coverage by 3.55%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3130      +/-   ##
==========================================
+ Coverage   57.09%   60.65%   +3.55%     
==========================================
  Files         299      308       +9     
  Lines       18731    29012   +10281     
==========================================
+ Hits        10695    17598    +6903     
- Misses       7166    10393    +3227     
- Partials      870     1021     +151     

[thaJeztah]

LGTM, thanks!

[acouvreur]

Any update on merge @thaJeztah ? 😄

[thaJeztah]

I guess this one dropped off my list; let me close/reopen to get a fresh run of CI