Write the telemetry events to a separate log

[3coins]

Problem

Current Telemetry handler is logging events to the server log, there is no option to write the telemetry events to a separate log.

Proposed Solution

• By default, write telemetry events to a separate file than the jupyter server log
• Provide an option to change the location of the telemetry log file

Additional context

[3coins]

cc @ellisonbg @jweill-aws