Add a config option to disable theme toggle buttons to automatically use browser settings

[caendesilva]

You can now disable the theme toggle buttons by setting theme_toggle_buttons to false in config/hyde.php.

If the Feature::Darkmode setting is disabled in the features array in the same file, this won't do anything, but if darkmode is enabled setting the theme toggle buttons setting to false they will not show up in the app layout nor the documentation layout; instead the appropriate color scheme will be automatically applied based on the browser system settings.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.97%. Comparing base (4f4c67c) to head (1dc8fe0).
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #1697   +/-   ##
=========================================
  Coverage     99.97%   99.97%           
- Complexity     1744     1746    +2     
=========================================
  Files           181      181           
  Lines          4663     4665    +2     
=========================================
+ Hits           4662     4664    +2     
  Misses            1        1           

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[caendesilva]

Note that if this is enabled for an existing site, if a user has previously used the toggle buttons they may still have a local storage setting that will take precedence. Clearing this would require changing the storage key (which we may want to do in a future release to prefix it with hyde) but we can't do that here as it's a breaking change.