API: new kwarg for return raw response

Historically we had duplicated method names with "async" that would return the response rather than a parsed astropy Table.

We agreed to clear this behaviour up (e.g. https://github.com/astropy/astroquery/issues/2598), but it also came up that having an easier access to the raw response can be useful (e.g. see the discussion in #3359).

So this is a formal issue to make the latter happen, we should add a `return_raw_response` or similarly named kwarg to the API rather than duplicating methods.

Let's brainstorm the kwarg first and then I recommend doing the API changes incrementally by adding the kwarg and in the same time removing the usage of the duplicating decorator.

Start by reading the discussion in issues #2598 and #3359, then inspect how the API currently uses duplicated methods and the duplicating decorator. Done means agreeing on a kwarg name and incrementally adding raw-response access while removing that duplicated-method usage.

Written by the indexing model from the issue text.