Lacking a method for identifying manufacturing instructions while in branch

[hraftery]

We don't have a documented method of providing unique identifiers to design files such as BOMs, so they can be identified when submitting to a third party (eg. a manufacturer) for processing. This has led to confusion about what version has been sent, regressions when re-submitting, and breakdowns when incorporating changes during the design process.

The de-facto identifier for design files in the master branch is the VERSION, provided by VersionBot. This works well. So the gap is design files that exist in a branch, such as during the lifetime of a PR.

A proposal was raised in this brainstorm topic. Over some discussion, the proposal was broadly acceptable, although no firm conclusion was made on the various questions it raises. In the interim, it probably serves as a useful guide and a dramatic improvement on no guide at all.