[Form]: Add controlled field hook

[vovakulikov]

Part of https://github.com/sourcegraph/sourcegraph/issues/47237
Preparation for https://github.com/sourcegraph/sourcegraph/pull/47572

This PR adds a new type of file hook - useControlledField. There are a few cases when we want to store the field's value, not in the form but somewhere else (like in another field store, or some external store) useControlledField doesn't bind with useForm it only adds a validation pipeline to the data; that consumer is supposed to provide.

Also, this PR fixes one small visual problem with insight creation UI (I didn't want to open yet another one-line PR for it)

Test plan

• Check that code insight creation UI works properly

App preview:

• Web

Check out the client app preview documentation to learn more.

[sg-e2e-regression-test-bob]

Bundle size report 📦

Initial size	Total size	Async size	Modules
0.00% (0.00 kb)	0.00% (+0.19 kb)	0.00% (+0.19 kb)	0.00% (0)

Look at the Statoscope report for a full comparison between the commits 01eea83 and 83746c1 or learn more.

Open explanation

• Initial size is the size of the initial bundle (the one that is loaded when you open the page)
• Total size is the size of the initial bundle + all the async loaded chunks
• Async size is the size of all the async loaded chunks
• Modules is the number of modules in the initial bundle

[valerybugakov]

Tested creation UI ✅