[RFE] Support Concurrent KVP Telemetry

Currently, the `tracing-subscriber` and general telemetry setup assumes all telemetry is emitted by azure-init. To better support external use, the tracing setup ought to allow libraries to initialize the subscriber with their metadata (ex: prefix with something other than `azure-init`).

This issue's goal is to bolster the current KVP setup to be more robust and support concurrent KVP emissions.