Make a design proposal for using gRPC interface

[manoranjith]

Motivation / Context

Define specification for and implement an RPC interface for node user.

Description

gRPC has been identified as the protocol for first implementation of RPC interface adapter. Document the rationale for choosing gRPC in a design proposal.

Relates to

Testing

-NA-

Thread Safety

-NA-

Acceptance Criteria

1. Design proposal is created, discussed and accepted.