Support all Gremlin message serializer formats for Neptune

[michaelnchin]

Issue #, if available: N/A

Description of changes:

• Support passing all GraphSON and GraphBinary TinkerPop serialization formats in the message_serializer field of %%graph_notebook_config.
• Enforce connection_protocol -> http for certain serializers unsupported by GremlinPython driver
• Change default connection_protocol from ws -> http, and message_serializer from graphsonv3 -> GraphSONUntypedMessageSerializerV1

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.