Build a forward looking strategy for trestle to support multiple oscal versions (potentially in the same codebase

[butler54]

Issue description / feature objectives

Today a bugfix change from NIST triggers a major change for trestle.

In an ideal world trestle versions should be able to support a range of minor and bugfix versions in the same codebase.

Caveats / Assumptions

Completion Criteria

• Current and forward looking strategy is documented.
• Issues for code buildout are generated.

[butler54]

One strategy could be to opportunistically upgrade document versions.

[butler54]

Do we need to be able to export at the same level as import or can we assume minor / bugfix oscal version bumps are okay for downstream tools?