Decide how semantic conventions for Entities should be defined

[jsuereth]

We will define a "how to model entities" guide for Semantic Convention to help existing SIGs with their resource modelling.

Example litmus test is-a design doc

[jsuereth]

Current proposal: https://docs.google.com/document/d/1GmB0kDx9opHxjj2oy6A4h0fqE8UVW-3ebWgp6zhtbVE/edit?tab=t.0

[jsuereth]

A (late) update that the proposal has been accepted and we're moving forwards with implementation within Weaver + Semconv.

[jsuereth]

Marking this closed in favor of the tracking bug