[RFC][DependencyInjection] Add separate section for named services generated through configuration

[codedmonkey]

For certain types of services in Symfony, it's possible to create named/scoped services, examples include:

• Scoped HTTP clients
• Namespaced cache pools
• Named serializers

Those named services can be referenced directly through dependency injection by naming and typing the dependency a certain way or by using the Target attribute. While this is amazing functionality that's already documented in the service container docs in the context of manually specifying service aliases, for the above use-cases it's explained differently for each one, and IMO it's difficult to understand unless you already know what's going on.

Should we make an additional part of the documentation specifically targeted at how to use aliased services that we can link from the above examples? I think this would improve DX