Create and release a golang RPC client

[mollykarcher]

What problem does your feature solve?

Several partners and ecosystem members have indicated a desire for a golang client of RPC. Horizon has horizonclient and txnbuild, and we'd like an analog to this for RPC. This may also assist some members of the ecosystem in migrating over their use cases from Horizon to RPC. This would also be beneficial for use in our own integration tests.

What would you like to see?

A release of a golang client that utilizes all endpoints available in the RPC.

Not required, but a nice-to-have would be how (and if) we could utilize openrpc; exploring if there's a way that we could autogenerate client code from the openrpc spec (similar to swagger codegen but for openrpc?).