test: add functional test for deprecatedrpc=fees

Test for old fields when `-deprecatedrpc=fees`
flag is passed and verify values in the deprecated
fields match values in the fees sub-object.

test/functional/test_runner.py

@@ -309,6 +309,7 @@ BASE_SCRIPTS = [
     'feature_presegwit_node_upgrade.py',
     'feature_settings.py',
     'rpc_getdescriptorinfo.py',
+    'rpc_mempool_entry_fee_fields_deprecation.py',
     'rpc_help.py',
     'feature_help.py',
     'feature_shutdown.py',