chore: extract buildSettingComponent method into a FormGroup component

[SychO9]

Changes proposed in this pull request:

• Extracts what the method does into a component reusable across all the admin panel. I pondered moving this to common to allow using on the forum frontend as well, but not sure if the use case for it exists, are there extensions that add forms as in the admin side that could benefit from this?

Necessity

• Has the problem that is being solved here been clearly explained?
• If applicable, have various options for solving this problem been considered?
• For core PRs, does this need to be in core, or could it be in an extension?
• Are we willing to maintain this for years / potentially forever?

Confirmed

• Frontend changes: tested on a local Flarum installation.
• Backend changes: tests are green (run composer test).
• Core developer confirmed locally this works as intended.
• Tests have been added, or are not appropriate here.

[luceos]

I remember having tried using this in the forum frontend at some point. So moving it to common would get an upvote from me.

[askvortsov1]

+1 on putting this in common if possible, this is way preferable to writing custom forms by hand.