Paths should be interpreted relative to config file

Currently, biotracker fails to execute components when it is executed from a different path then the config file:

Running `target/release/biotracker4 --config ../biotracker-pkg/config.json --realtime false --force-camera-config acA2040-90um --video /home/max/projects/sleap/tracked_videos/following4_annotated.mp4`
/bin/sh: line 1: biotracker-venv/bin/activate: No such file or directory
/bin/sh: line 1: biotracker-venv/bin/activate: No such file or directory