Add support for the Rosetta API

[mdyring]

https://www.rosetta-api.org/

Cosmos SDK already has support for it:
https://docs.cosmos.network/master/run-node/rosetta.html

[blewater]

Shipping beta in the upcoming sdk release v0.43
https://github.com/cosmos/cosmos-sdk/blob/v0.43.0-rc1/RELEASE_NOTES.md#rosetta-beta-feature

Rosetta (Beta Feature)

Rosetta is an open standard of API endpoints designed to simplify blockchain deployment and interaction. It is maintained by Coinbase and used by their team to integrate various blockchains within their exchange platform. In order to facilitate integrating Cosmos-based chains with third-party services using Rosetta, the Cosmos SDK natively supports Rosetta via the {appd} rosetta CLI command, which runs a Rosetta API server as a sidecar.

Please note that this feature is still in the beta phase, and rough edges will be polished in the next releases.