This PR improves the logging for tari_mining_node by making use of the log4rs target, it also sets the default logging level to info.
This PR also adds basic statistics for pool mining which are automatically displayed on a 20s interval.

Review comments
Add additional log target, split logging messages between terminal and file.
Updated stratum miner to display basic statistics every 20 seconds instead of when changing jobs.
Added info message to indicate hashing is in progress for stratum miner.
Added hash rate to displayed statistics in additon to share rate.
Included metric for share and hash rates.

Error handling for rejected share