feat: Add ability to set default theme for UI

[Jamess-Lucass]

resolves issue: #1952.

As part of this PR I changed the initial theme values from light to system which should better fit a default. eg.
ui/src/app/preferences/preferencesSlice.ts#L15 and ui/src/app/preferences/Preferences.tsx#L47.

Please let me know if you want this reverted back to light.

If this is accepted I can open a PR in flipt-io/docs to add this configuration value to https://www.flipt.io/docs/configuration/overview#general

[markphelps]

Thanks @Jamess-Lucass !! Works great if user doesn't already have theme set (which is what we want)

FLIPT_UI_DEFAULT_THEME='system' ./bin/flipt

[GeorgeMac]

This PR is looking great @Jamess-Lucass ! Just incase it isn't clear, we have a couple schema's around our configuration file which need to be valid. That is whats failing during CI.

--- FAIL: Test_JSONSchema (0.01s)
    schema_test.go:63: 
        	Error Trace:	/src/config/schema_test.go:63
        	Error:      	Should be true
        	Test:       	Test_JSONSchema
        	Messages:   	Schema is invalid
    schema_test.go:65: ui: Additional property default_theme is not allowed

• JSON Schema: https://github.com/flipt-io/flipt/blob/main/config/flipt.schema.json
• CUE Schema: https://github.com/flipt-io/flipt/blob/main/config/flipt.schema.cue

These need to be updated to include your new string field.
Happy to give pointers if you're unfamiliar with either of these schema languages.

[Jamess-Lucass]

This PR is looking great @Jamess-Lucass ! Just incase it isn't clear, we have a couple schema's around our configuration file which need to be valid. That is whats failing during CI.

--- FAIL: Test_JSONSchema (0.01s)
    schema_test.go:63: 
        	Error Trace:	/src/config/schema_test.go:63
        	Error:      	Should be true
        	Test:       	Test_JSONSchema
        	Messages:   	Schema is invalid
    schema_test.go:65: ui: Additional property default_theme is not allowed

• JSON Schema: https://github.com/flipt-io/flipt/blob/main/config/flipt.schema.json
• CUE Schema: https://github.com/flipt-io/flipt/blob/main/config/flipt.schema.cue

These need to be updated to include your new string field. Happy to give pointers if you're unfamiliar with either of these schema languages.

Ahh, thanks for pointing me in that direction, I've made those changes and run schema_test.go locally and they're passing.

[markphelps]

@all-contributors please add @Jamess-Lucass for code

[allcontributors]

@markphelps

I've put up a pull request to add @Jamess-Lucass! 🎉

[markphelps]

Looks great @Jamess-Lucass !! thank you for the contribution!

[codecov]

Codecov Report

Merging #2062 (721b9e9) into main (a8ffa95) will increase coverage by 0.00%.
Report is 1 commits behind head on main.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #2062   +/-   ##
=======================================
  Coverage   70.41%   70.41%           
=======================================
  Files          70       70           
  Lines        6820     6822    +2     
=======================================
+ Hits         4802     4804    +2     
  Misses       1741     1741           
  Partials      277      277           

Files Changed	Coverage Δ
internal/config/config.go	87.00% <100.00%> (+0.03%)	⬆️
internal/config/ui.go	100.00% <100.00%> (ø)

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[markphelps]

awesome! thanks again!