This commit changes how RestHandlers are registered with the
RestController so that a RestHandler no longer needs to register itself
with the RestController. Instead the RestHandler interface has new
methods which when called provide information about the method and path
combinations that are handled by the handler including any deprecated
and/or replaced combinations.

This change also makes the publication of RestHandlers safe since they
no longer publish a reference to themselves within their constructors.

Closes elastic#51622