Enabled options to disable Omex telemetry via config

[artempushkin]

This opens the way to disable Omex telemetry implementations.

OmexLogger can be controlled by standard logging configuration, usually found in appsettings.json. Option class to disable generation of TimedScope metrics from Activities already existed, binding was improved with validation on start.

To disable both logs and activity metrics, put the following in appsettings.json:

{
  "Monitoring": {
    "ActivityEventSenderEnabled": false
  },
  "Logging": {
    "Omex": {
      "LogLevel": {
        "Default": "None"
      }
    }
  }
}

Initialization logger for now remains enabled, its usage should be reduced first.