Implement API browsers as a concern

[Kaliumhexacyanoferrat]

As a developer of a web service, I would like to add API browsers to a Inline handler.

Example

It feels counter-intuitive that .AddRedoc() and similar just work on layouts.

Inline.Create()
      .Get(() => "Hello World")
      .AddOpenApi() // works
      .AddRedoc(); // throws

Acceptance criteria

• API browsers can be used as regular concerns
• The change is backwards compatible
• The documentation is updated