CAMEL-10809 Introduce configurator SPI for rest support in camel-core

[zregvart]

This removes the SwaggerRestProducerFactory and moves the
responsibility of configuring rest clients to a new SPI
(RestEndpointConfigurer).

The rest endpoint URI has been changed to allow for syntax like:

rest:<component>[:componentSpecific]

Or in case of Swagger:

rest:swagger:getPetById?apiDoc=petstore.json

The SPI is discovered in the META-INF/services/org/apache/camel/rest
properties file with the prefix configurer. so any other components
wishing to configure rest endpoints via this configurer SPI should add
rest file with configurer.class property.

I would like feedback on the following issues:

• instead of META-INF/.../rest use different properties file?
• design of the RestEndpointConfigurer SPI interface (for instance: is
  it sufficient so that it can be used to plug in headers, or
  authentication callbacks for rest)
• integration with service discovery ({{service:...}})?
• properties missing from Swagger specification (notably host, and
  port) -- current idea is that that should be provided from
  RestConfiguration

[davsclaus]

I have a bit doubt about the rest swagger stuff I did, and why it was so generic.
The drawback with making this so generic is that

• bad tooling support
• a bit confusing to use (too generic)
• only 1 implementation of api-doc = swagger. Not really seeing that there are many other alternatives out there

I wonder if we have rest-swagger as component instead of rest:swagger: etc. Then it can make it stand out as a component and its just like any other component.

I would like if you can look into that. The rest-swagger may built on top of the generic stuff we have now/you have, but from end users they should use rest-swagger so we have it as a 1st class component and also available from the camel-catalog / documentation / component list et all.

[zregvart]

Thanks @davsclaus let's try to go down that route