Configurable ffmpeg

[NickM-27]

This adds an ffmpeg path config and adjusts the installation to include the current stable ffmpeg as well as ffmpeg 7. This will:

• allow users to easily switch to ffmpeg 5 if ffmpeg 7 is causing issues on their system
• switch back and forth for easier debugging
• use custom ffmpeg builds without needing to use a bind mount

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[chrislawso]

is this change meant to release for 0.15 or also 0.14.x ?

[NickM-27]

0.15