[build] what is best-practice for setting "job_prefix"?

### Description

I've been searching docs and old tickets, and can't find any examples of best-practices for setting job_prefix.
It will vary by corporation, site and project. So it shouldn't go into the repos itself. I'm assuming that it should be set using an environment variable, but it's always dangerous to "assume".
If the docs already say how to use it, could you please point me to it?
If not, could you please add something to the docs, and point me to it?

Search the repository documentation and build configuration for existing references to job_prefix and any environment-variable guidance. Confirm how it is intended to be set and document the corporation, site, or project-specific best practice; done means the guidance is published in the appropriate docs location and can be linked from this issue.

Written by the indexing model from the issue text.