Update registry rest client to support bearer authentication

Author: gtato

src/confluent_kafka/schema_registry/schema_registry_client.py

@@ -111,7 +111,10 @@ def __init__(self, conf):
                 raise ValueError("basic.auth.user.info must be in the form"
                                  " of {username}:{password}")
 
-        self.session.auth = userinfo if userinfo != ('', '') else None
+            self.session.auth = userinfo
+        elif 'token' in conf_copy:
+            token = conf_copy.pop('token')
+            self.session.headers['Authorization'] = f'Bearer {token}'
 
         # Any leftover keys are unknown to _RestClient
         if len(conf_copy) > 0: