Allow to set headers and parameters in all requests

[lbalmaceda]

Changes

All the methods of both API clients now return a request instance that supports being set headers and additional parameters, without the need of casting them to a different class.

• Methods returning Request now return ParameterizableRequest, exposing both customization methods. This fixes the use case for all the UsersAPIClient and 40% of the AuthenticationAPIClient.
• Adds a new interface AuthRequest that extends the existing AuthenticationRequest, which already supported adding parameters, and now supports adding headers.
• DelegationRequest, SignUpRequest, and ProfileRequest got these methods added.
• SignUpRequest and ProfileRequest got the existing constructor deprecated to signal that when used, the headers are not customizable. They were only used internally on 3 occasions across the AuthenticationAPIClient class.

There are code formatting changes among the diff, apologies in advance if that generates noise.

References

#314 / ESD-7306

Testing

• This change adds unit test coverage

• This change adds integration test coverage

• This change has been tested on the latest version of the platform/language or why not

Checklist

• I have read the Auth0 general contribution guidelines

• I have read the Auth0 Code of Conduct

• All existing and new tests complete without errors