Document what different states mean (e.g "eaten")

**Describe the enhancement**
Being new to the OpenCue, there is a few references to "eating frames", and I couldn't work out exactly what that means (and thus things like the "Eats all dead frames for job" pacman button in the cuegui were mysterious)

Only as I write this I stumbled across the docstrings on
https://github.com/AcademySoftwareFoundation/OpenCue/blob/d2057d3f1c3c01d5a78fedd9a22fe8400d91ec83/proto/job.proto#L409-L427
which explains it nicely, "Frame is eaten, acts like the frame has succeeded" - although a little more context would be helpful (like I the state exists to allow dependent jobs to continue, unlike leaving the frames as dead?)

Would be handy to have the states this documented in the glossary or similar

**Screenshots**
~If applicable, add screenshots to help explain your suggestion.~

**Version Number**
d2057d3f1c3c01d5a78fedd9a22fe8400d91ec83

**Additional context**
~Add any other context here.~

Start with the state docstrings in proto/job.proto around lines 409-427, then inspect the existing glossary or related documentation and the CueGUI context for the Pacman action. Document what the relevant states mean, including why eating a frame lets dependent jobs continue, and make the Pacman action understandable to newcomers.

Written by the indexing model from the issue text.