Change .FIT file metadata to indicate Zwift-specific recording device when user rides with zPower

*** Issue ***
.fit files generated by the application contain metadata indicating the activity was recorded with a Garmin Edge 500. For users who cheat (e.g. by using multiple spoke magnets to inflate zPower) it becomes nearly impossible for Strava staff/users to identify truly faulty segments.

*** Proposed Resolution ***
When a user is riding with zPower, change the metadata to indicate a recording device that is specific to Zwift so that erroneous segments and rides can be more easily identified and verified on Strava.