[feature-request] Provide .tlog files for download

[rafaellehmkuhl]

Applications that were directly connected to mavlink routers were able to generate .tlog files from those, as they had direct access to raw mavlink messages.

This is not the case for applications connected to mavlink2rest, as they receive parsed JSON messages.

My proposal is that mavlink2rest stores the raw data in a .tlog file and provide an endpoint, so we can retrieve this file.

The ideal case is that the file is downloadable even if mavlink2rest is already running, so we don't have to restart it to have access to the file.

Naturally, it would be good if it also allowed specifying the destination folder for the files.