enh(io): add a way to set the video grabber loop mode by a generic parameter

Description

This adds a way to set the loop mode in a video grabber using a parameter. The only way so far was to use a toggle slot which is not really convenient.

This also overrides the new configuring(const config_t&) signature in tracker interface to allow implementations to override it as well (otherwise you get a compile error).

How to test it?

Used in depending merge-request.