Rename mm2 into jsonrpc

[onur-ozkan]

We no longer use the "mm2" naming for this project since the KDF renaming but RPC payloads still include the "mm2" field. We should rename it to "jsonrpc" without breaking existing systems. To do that, we can support both "mm2" and "jsonrpc" at the same time and keep the "mm2" support for at least a year with displaying a warning whenever "mm2" is used instead of "jsonrpc".

[DioBr4nd0]

hii @onur-ozkan I would like to work on this issue. Can you please assign this to me?

[onur-ozkan]

No need to assign the issue - Feel free to send a PR and ping me there :)