Create examples for retrieving payFees for a transaction and for dry-run executions

Hello team,

Can you please include some examples for:

-  Retrieving payFees for a transaction 
-  Execute dry-run executions

I have been checking the docs, but it's not correct, it looks like subxt::rpc module is the one to be used but it's not there

It looks like the real rpc methods are in subxt::backend::legacy::rpc_methods


Thank you