Consider relying on CometBFT's rpc/http client

[cason]

I have the impression (close this issue if it is not the case) that this tool implements by itself the interaction via RPC with Comet nodes, to submit load and other functionalities.

We should instead use one of the existing RPC client implementations in Comet. In particular because, in this case, we don't need to maintain another version here.

I think that one of reasons for this local implementation, however, is the fact that CometBFT repo imports this repo, so that importing CometBFT here would cause an import loop. Not sure how easy is to prevent this loop.