Users wanting to send a request by providing only its method and endpoint, effectively the only two required arguments, shouldn't need to pass in an empty map and a null entity for the body. While at it we can also add a variant to send requests by specifying only method, endpoint and params, but not body. Headers remain a vararg as last argument, so they can always optionally be provided.
Closes#19312
:client ---------> :client:rest
:client-sniffer -> :client:sniffer
:client-test ----> :client:test
This lines the client up with how we do things like modules and
plugins.