Add timeout param to ledger interactions

[0xArdi]

          This is duplicated on purpose to avoid introducing deps between the contracts. I think it should ultimately be something offered by the ledger connection, as it already is executing these ledger interactions in a ThreadPoolExecutor. 

I think we should extend the current contract_api and ledger_api protocol to include an optional timeout field.

Originally posted by @0xArdi in valory-xyz/trader#168 (comment)