Support arbitrary axiom annotations

For many use cases we need to be able to add provenance on axioms. I have zero ideas about the syntax, here is some pseudo code:

add axiom-annotation sssom:object_label "sarcoma" to { MONDO:123 oboInOwl:hasDbXref "DOID:123"}

The issue provides only pseudo-code and names no files, tests, or entry points. Start by locating the KGCL syntax and axiom model, then determine the annotation syntax and representation needed for arbitrary axiom annotations. Done means the proposed form is supported and covered by tests for the shown provenance example.

Written by the indexing model from the issue text.