Add better logging and metric collection

[abizjak]

Task description

The wallet-proxy does not record any metrics about the response latencies but it would be valuable to have them. Similarly, logging is sometimes inadequate for issue analysis.

• Record or log response latencies. Logging would already be valuable, but the ideal would likely be to expose them in a standard way like we do with the node, so via Prometheus.
  • Response time from database queries to the transaction log database.
  • Response time for node queries.
• Log additional data with requests.
  • For account creation transactions (in submitCredential) log the address of the account that would be created.
  • For transaction submission log the sender account (and maybe some other items from the header such as expiry and nonce).