Move rpc folder to ethermint fork

[skosito]

Describe the Issue Currently rpc folder in repo is forked from ethermint. Now when there is ethermint fork, changes can be moved there and folder can be deleted from main repo. This will make code more focused and easier to maintain and issues like https://github.com/zeta-chain/node/issues/1959 easier to navigate and fix.

Expected Outcome Rpc changes moved to ethermint fork, or documented why it's not possible.