Allow the telemetry to be "burnt" to the video during processing

This is ofter asked by users, so they can skip having to do that in Handbrake afterwards.

We could also put this as a post-processing pipeline to be done manually (click a button, select the video and .ass file and they will be merged).

The issue names telemetry, video processing, Handbrake, and .ass files, but no repository entry point or test. First clarify whether this should be automatic processing or a manual post-processing action, and define the supported inputs, outputs, and workflow. Done means telemetry is burned into the video through the agreed workflow.

Written by the indexing model from the issue text.