Add Websocket "config entries" methods

[mj23000]

Add most of the Websocket methods available in the config_entries.py file.

Missing from this PR so far:

• ~Add testing for the newly added methods~
• ~Add config_entries/subscribe method~
• Ensure that get_entry_subentries and delete_entry_subentry work as intended

This PR also tweaks how the from_json() methods are used, so some feedback would be appreciated.

Kind regards

[mj23000]

I've added the missing method and testing for the new code.

[codecov[bot]]

Codecov Report

:x: Patch coverage is 99.57806% with 1 line in your changes missing coverage. Please review. :white_check_mark: Project coverage is 97.63%. Comparing base (e3ea524) to head (c8ec47f). :warning: Report is 4 commits behind head on dev.

Files with missing lines	Patch %	Lines
homeassistant_api/models/events.py	87.50%	1 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #213      +/-   ##
==========================================
+ Coverage   97.44%   97.63%   +0.18%     
==========================================
  Files          25       26       +1     
  Lines        1647     1864     +217     
==========================================
+ Hits         1605     1820     +215     
- Misses         42       44       +2     

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