feat!: remove create plugin support

[erisu]

Motivation, Context & Description

Resolves #118
Closes #119
Resolves #120
Resolves #121
Closes #122
Resolves #125

The tickets above report various issues related to the plugin creation functionality and the associated platform feature, which is tied to plugin development.

This area appears to be buggy, has not been maintained since 2019, and lacks proper documentation. Given this, I believe it is appropriate to remove it in the next major release.

Additionally, the Cordova dev documentation had significantly improved the plugin creation guide which does not reference plugman.

Several suggestions from the referenced tickets include:

• Creating a dedicated plugin template repository.
• Providing a clear, up-to-date documentation for plugin creation (which exists on the website).
• Deprecating the current plugin creation feature entirely.

Since the website contains an up-to-date documentation for plugin creation, the goal of this PR is to removing the feature completely. The guide on the website would be its replacement.

Testing

• npm t

Checklist

• I've run the tests to see all new and existing tests pass
• I added automated test coverage as appropriate for this change
• Commit is prefixed with (platform) if this change only applies to one platform (e.g. (android))
• If this Pull Request resolves an issue, I linked to the issue in the text above (and used the correct keyword to close issues using keywords)
• I've updated the documentation if necessary

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 63.63%. Comparing base (6b56211) to head (5ef5b32).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #166      +/-   ##
==========================================
+ Coverage   53.84%   63.63%   +9.79%     
==========================================
  Files           4        4              
  Lines          78       66      -12     
==========================================
  Hits           42       42              
+ Misses         36       24      -12     

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