ACI: Make querying links and nodes possible (#43441)

This functionality was not considered when the module was written, but
there's no reason why it shouldn't be supported.

We had to rework the query string construction and object filtering.
This new functionality allows to filter on arbitrary keys and supports
None values.

This PR fixes various issues with the existing framework, including
querying specific objects using construct_url_4 (i.e.
aci_epg_to_contract and aci_static_binding_to_epg)

lib/ansible/modules/network/aci/aci_firmware_source.py

@@ -236,8 +236,8 @@ def main():
         root_class=dict(
             aci_class='firmwareOSource',
             aci_rn='fabric/fwrepop',
-            filter_target='eq(firmwareOSource.name, "{0}")'.format(source),
             module_object=source,
+            target_filter={'name': source},
         ),
     )
     aci.get_existing()