docs: dedicated custom components docs (#10987)

Adds a dedicated "Custom Components" section to the docs.

As users become familiar with building custom components, not all areas
that support customization are well documented. Not only this, but the
current pattern does not allow for deep elaboration on these concepts
without their pages growing to an unmanageable size. Custom components
in general is a large enough topic to merit a standalone section with
subpages. This change will make navigation much more intuitive, help
keep page size down, and provide room to document every single available
custom component with snippets to show exactly how they are typed, etc.

This is a substantial change to the docs, here is the overview: 

- The "Admin > Customizing Components" doc is now located at "Custom
Components > overview"
- The "Admin > Views" doc is now located at "Custom Components > Custom
Views"
- There is a new "Custom Components > Edit View" doc
- There is a new "Custom Components > List View" doc
- The information about root components within the "Admin > Customizing
Components" doc has been moved to a new "Custom Components > Root
Components" doc
- The information about custom providers within the "Admin > Customizing
Components" doc has been moved to a new "Custom Components > Custom
Providers" doc

Similar to the goals of #10743, #10742, and #10741.

Fixes #10872 and initial scaffolding for #10353.

Dependent on #11126.

This change will require the following redirects to be set up:

- `/docs/admin/hooks` → `/docs/admin/react-hooks`
- `/docs/admin/components` → `/docs/custom-components/overview`
- `/docs/admin/views` → `/docs/custom-components/views`