feat: Update default rollout

[markphelps]

Re: #3300 (comment)
Closes: #2811

1. Make default rollout rule work like default variant does now (via form in rule itself)
2. Remove enabled toggle for boolean flags as it was confusing, move it to default rollout rule
3. Move some components that were in the ui/app folder to proper places in ui/components

TODO

• Add UI tests specific to default values
• Add UI tests for switching tabs (Variants, Rules/Rollouts, Analytics) (I broke this previously without realizing it)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 64.18%. Comparing base (713b3c1) to head (4036653).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3301   +/-   ##
=======================================
  Coverage   64.18%   64.18%           
=======================================
  Files         168      168           
  Lines       13506    13506           
=======================================
  Hits         8669     8669           
  Misses       4174     4174           
  Partials      663      663           

Flag	Coverage Δ
unittests	64.18% <ø> (ø)

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[erka]

Works great!