Better gamma log filtering

[vistra]

Gamma logs are very noisy - internal network maintenance and prism requests are polluting the log. Today there is a hard coded phrase based filter in the logger (https://github.com/orbs-network/orbs-network-go/blob/fee2cd60c5edb6d3fc4d64f599e3fb4824d4ce54/bootstrap/gamma/server.go - GetLogger()). I suggest to remove this logic from the logger and have gamma emit the full log. Instead the logs should be filtered out externally (e.g. using grep). We can provide a set of commands for convenient log filtering.