Migrate plugin type settings to plugin rez configs

[BryceGattis]

Migrate plugin type settings to plugin rez configs so we can more easily add plugin settings to our documentation.

This change is based on JC's suggestion here.

[JeanChristopheMorinPerso]

I'm curious to know what would happen if we removed this entirely from here.

[BryceGattis]

Running rez config plugins is how I've been verifying that my changes are working. Removing this line and attempting to run rez config plugins causes an error:

Traceback (most recent call last):
  File "e:\code\rez\venv\Lib\site-packages\rez\cli\config.py", line 53, in command
    data = data[key]
           ~~~~^^^^^
KeyError: 'plugins'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<frozen runpy>", line 198, in _run_module_as_main
  File "<frozen runpy>", line 88, in _run_code
  File "E:\Code\rez\venv\Scripts\rez\rez.exe\__main__.py", line 7, in <module>
  File "e:\code\rez\venv\Lib\site-packages\rez\cli\_entry_points.py", line 69, in run_rez
    return run()
           ^^^^^
  File "e:\code\rez\venv\Lib\site-packages\rez\cli\_main.py", line 189, in run
    returncode = run_cmd()
                 ^^^^^^^^^
  File "e:\code\rez\venv\Lib\site-packages\rez\cli\_main.py", line 181, in run_cmd
    return func(opts, opts.parser, extra_arg_groups)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "e:\code\rez\venv\Lib\site-packages\rez\cli\config.py", line 55, in command
    raise ValueError("no such setting: %r" % opts.FIELD)
ValueError: no such setting: 'plugins'

[JeanChristopheMorinPerso]

Tests should pass if you rebase your branch.

[linux-foundation-easycla]

• ✅ login: BryceGattis (7fd86e2, 083507a, 090578a, 90dbc25)
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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 58.39%. Comparing base (36e0537) to head (090578a).
Report is 12 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1746      +/-   ##
==========================================
+ Coverage   58.29%   58.39%   +0.10%     
==========================================
  Files         126      126              
  Lines       17159    17163       +4     
  Branches     3505     3506       +1     
==========================================
+ Hits        10002    10023      +21     
+ Misses       6493     6474      -19     
- Partials      664      666       +2     

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