cli/command, cli-plugins/plugin: some cleanups in WithInitializeClient, withPluginClientConn

[thaJeztah]

• taken from [WIP] untangling auth-related code #5925

---

• cli/command: move WithInitializeClient to other options
• cli/command: make WithInitializeClient a wrapper for WithAPIClient
• cli-plugins/plugin: rewrite withPluginClientConn w/ WithAPIClient
  The WithInitializeClient looks redundant altogether, so let's rewrite this function to not depend on it.

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[codecov-commenter]

Codecov Report

Attention: Patch coverage is 28.57143% with 10 lines in your changes missing coverage. Please review.

Project coverage is 55.02%. Comparing base (8e5fb5b) to head (240b069).
Report is 69 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6081   +/-   ##
=======================================
  Coverage   55.02%   55.02%           
=======================================
  Files         361      361           
  Lines       30126    30131    +5     
=======================================
+ Hits        16578    16581    +3     
- Misses      12594    12595    +1     
- Partials      954      955    +1     

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