[Feature request] Add option for YouTube's (toggable and not DNS level) restricted mode

[syeopite]

Is your feature request related to a problem? Please describe. YouTube offers a togglable restricted mode to filter out mature content.

Describe the solution you'd like

A option to enable this restricted mode should be added to Invidious.

Describe alternatives you've considered

Additional context

Related #2487

[retronym]

FreeTube implements a parental control feature by passing enable_safety_mode=true to the innertube.create API. https://github.com/FreeTubeApp/FreeTube/pull/1456/files https://github.com/LuanRT/YouTube.js/blob/6bb2086875d089f47c5f86ce94db9e32cb051319/README.md#L128

I'm not sure of the differences between this API option and the DNS-based filtering.

Another useful link is the "YouTube content restrictions settings / Check if YouTube content restrictions are turned on" page:

https://www.youtube.com/check_content_restrictions