eth_newPendingTransactionFilter needs to be implemented

[tclemos]

Since the tx pool is centralized, we decided to deprecate the current implementation and for now, the code is not implementing this endpoint.

As soon as we finish defining how we are going to manage the pool, we need to implement this for HTTP and WS requests.

[tclemos]

This is blocked at the moment until we define what to do related to having a shared pool.