Currently feature flags can be enabled for anonymous or logged in users. Going forward we'd like to make it possible to roll features like dark mode out to logged in users as beta feature.
e.g.
```
$wgVectorClientPreferences = [
"logged_in" => false,
"logged_out" => false
];
```
Going forward it would be useful to mark features as available in a set of beta features.
e.g. it should be possible to enable the settings cog to beta feature users.
```
$wgVectorClientPreferences = [
"logged_in" => false,
"logged_out" => false,
"beta" => false
];
```
# TODO (Spec)
[x] A beta feature is added to Special:Preferences for Vector 2022 beta:
{F37854331}
[x] When a feature sets the key "beta_feature" to true, it is enabled to users who have the beta feature enabled.
[x] If BetaFeature extension is disabled, configuration flags marked as beta_feature will not be loaded regardless of when they are true
[x] Beta feature should be configurable and default to off (does not appear on the list of the beta features)