Add custom location for OpenImageIO and FFMpeg

[antirotor]

Feature

We should add option to set custom path OpenImageIO binaries and ffmpeg. This would allow adventurous TDs to use their own custom builds.

Proposal

Add option to System Setttings to set those paths. If set, use those.

Question: Do we need it per project?

Related #3858

[cuID:]

[m-u-r-p-h-y]

I was testing ffmpeg 5 and there were a lot of issues with some deprecated arguments we use with our older build, so maybe per project toggle to use custom paths would allow us not to break running production when testing these custom builds..