feat: Add Callback DataStream

[samcm]

• Adds a new callback DataStream that implements the DataStream interface similar Kinesis
  • Allows other Go projects to start a Hermes Node instance directly and to receive events.
  • Unsure if we want to generalize it even further with some config to toggle which DataStream's are enabled. At the moment it's toggled by the existence of aws config.
• Makes the RpcMeta structs public for easy consumption in other Go projects

Related Xatu integration: https://github.com/ethpandaops/xatu/pull/297

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[samcm]

Thanks @guillaumemichel! This one is ready for review I think. I've tested it against a localstack Kinesis and it looked ok but I've never really used Kinesis before so not entirely sure what to test against. I could produce/consume messages at least. cc @cortze 🙏

[samcm]

Should be all good now @cortze, thank you!