CoAP Gateway for Hyperledger Fabric (#66)

* CoAP Gateway for Hyperledger Fabric RFC

- Added a new RFC proposing a CoAP gateway to enable IoT and resource-constrained devices to interact with Fabric networks.
- Defined lightweight, UDP-based communication using CoAP protocol with DTLS security for encrypted and authenticated connections.
- Outlined the gateway architecture as an optional peer service that acts as a protocol converter.
- Included four core endpoints: /evaluate, /endorse, /submit, and /events for transaction operations.
- Provided integration with existing Fabric MSP for device identity management and X.509 certificate authentication.
- Ensured backward compatibility by making the CoAP gateway an optional feature that doesn't affect existing gRPC gateway functionality.
- Added comprehensive error handling with appropriate CoAP response codes and security model integration.
- Included example use cases for supply chain tracking and smart city applications with IoT sensors.

Signed-off-by: bernardo.figueiredo <[email protected]>

* Improve markdown formatting and readability

- Standardizes the document structure to improve readability
- Standardizes heading levels and adds consistent spacing between sections
- The technical content remains unchanged, but the overall document is now more consistent and easier to read.

Signed-off-by: bernardo.figueiredo <[email protected]>

* Add CommitStatus endpoint to CoAP Gateway RFC

- Add /commit-status endpoint with SignedCommitStatusRequest/CommitStatusResponse
- Clarify submit behavior: waits for orderer submission
- Update endpoint count and API documentation for complete gateway parity
- Add CommitStatusHandler to core components

Enables IoT devices to check transaction status asynchronously after submission.

Signed-off-by: bernardo.figueiredo <[email protected]>

* Switch CoAP Gateway to protoc plugin with dual-cert security

Key changes:
- Automated client generation via protoc plugin
- Clarify dual-certificate model follows standard Fabric pattern
- Update endpoints to RPC-style (/rpc/gateway.Gateway/{Method})
- Add implementation details (peer lifecycle, context flow, error mapping)
- Add developer experience section with code examples
- Remove duplicate MSP configuration (uses peer-level config)
- Streamline security explanations to emphasize consistency with gRPC

Signed-off-by: bernardo.figueiredo <[email protected]>

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Signed-off-by: bernardo.figueiredo <[email protected]>

Author: bernardo-rf