Joystream Rosetta API support

# Background
[Rosetta](https://www.rosetta-api.org/) is a standard for how to allow infrastructure providers (e.g. custodians, exchanges, hosted wallets) to integrate with a new chain with minimal overhead, and it is widely adopted and supported. Having such support and documentation for the Joystream chain would be useful. There seems to already be work done on Substrate support for this API, here are some references

* https://blog.edgewa.re/edgeware-community-implements-rosetta-api-for-substrate/
* https://github.com/edgeware-network/substrate-rosetta-api

# Proposal
* Review Rosetta API
* Review status of completed work by Edgeware, in particular whether it is production ready.
* Compile list of enhancements or adaptations that may be needed for Joystream
* Prepare whatever documentation is needed for third parties to get up and running with Rosetta+Joystream.

┆Issue is synchronized with this [Asana task](https://app.asana.com/0/1201958687417145/1203148367240804) by [Unito](https://www.unito.io)