rgw: store RGWEndpoint URL as boost::urls::url

rgw: store RGWEndpoint URL as boost::urls::url

Replace raw string manipulation in RGWEndpoint with boost::urls::url.
URL path/query/host changes now use set_path(), set_query(), set_host()
instead of string concatenation.

Rename original_url to endpoint_url_lookup_id to clarify its role as a
health-tracking key for ResolvedEndpoint lookup in
set_endpoint_unconnectable().

Signed-off-by: Oguzhan Ozmen <oozmen@bloomberg.net>