Fix serialization of repeated fields with empty messages (#180)

Extend test config and utils to support exclusion of certain json samples from
testing for symetry.

tests/inputs/config.py

@@ -19,3 +19,10 @@ services = {
     "example_service",
     "empty_service",
 }
+
+
+# Indicate json sample messages to skip when testing that json (de)serialization
+# is symmetrical becuase some cases legitimately are not symmetrical.
+# Each key references the name of the test scenario and the values in the tuple
+# Are the names of the json files.
+non_symmetrical_json = {"empty_repeated": ("empty_repeated",)}