Feature request: Allow custom post-processing shell script

[Darkness4]

Could be used to transcode the raws.

This would be run after remux/concat.

This need to be documented:

• "Keep intermediates" to be able to post process on raws
• Using ".combined." to be able to post process on concatenated files
• A guide to preview the rendered script.

To help the user on the post-processing script, we should inject variables (to be determined).

Distroless containers has obviously no way of post-processing scripting. It's up to the user to add their own OS (or up to me to upload a container".