Add Prometheus Metric for Tracking File Size

[evanugarte]

In the below line, lets add a metric to track file size for prometheus:

Quasar/printer/server.py

Line 137 in ca5a8ad

f.write(await file.read())

Once done, check if the file recieved in chunks or all at once. If it is the former, lets add a metric to track data rate.