Remove sudo dependency

[daniil-berg]

To somewhat mitigate the potential security vulnerability that comes from running third-party programs like ffmpeg as sub-processes, we currently provide the check_user config option that makes Videbo launch those sub-processes with sudo -u <check_user> <command>.

This is not a particularly elegant way to solve the underlying issue and forces Videbo to rely specifically on sudo as a dependency for this functionality.

There are different sandboxing tools out there (e.g. Bubblewrap) that could be used to run those programs more safely and we should leave the choice to the user.

The entire check_user logic and the config option should be removed. sudo should be removed as requirement from the documentation. Instead a working example configuration with something like Bubblewrap should be provided to demonstrate how a more secure setup could look.