[enhancement] Make the Digital Twin Graph Service support other protocols

[ashbeitz]

Description

The Digital Twin Graph Service supports interaction with the digital twin via RPC. It needs to support other protocols, like MQTT and streaming.

Here are some initial ideas on how this may be done (there are probably more):

• It can use the instance IDs discovered when interacting with the Digital Twin Graph to lookup the associated entity access info in the Digital Twin Registry.
• The values returned by Find and Get interactions with the Digital Twin Graph could include the entity access info.

Acceptance criteria

• Criteria 1
• Criteria 2
• Criteria 3
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