Enforce oscal version in models and tests

[fsuits]

Now enforce oscal version defined in one place. Many changes to tests and data.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.
• All commits are signed-off.

Now enforce oscal version defined in one place in code. This involved modifying the base models generated along with many tests and sample data sets.

[codecov]

Codecov Report

Merging #377 (aa0f6ae) into develop (52a49db) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff            @@
##           develop     #377   +/-   ##
========================================
  Coverage    98.91%   98.91%           
========================================
  Files           56       56           
  Lines         6632     6636    +4     
========================================
+ Hits          6560     6564    +4     
  Misses          72       72           

Impacted Files	Coverage Δ
trestle/core/generators.py	97.26% <100.00%> (+0.11%)	⬆️
trestle/oscal/__init__.py	100.00% <100.00%> (ø)
trestle/oscal/assessment_plan.py	100.00% <100.00%> (ø)
trestle/oscal/assessment_results.py	100.00% <100.00%> (ø)
trestle/oscal/catalog.py	100.00% <100.00%> (ø)
trestle/oscal/component.py	100.00% <100.00%> (ø)
trestle/oscal/poam.py	100.00% <100.00%> (ø)
trestle/oscal/profile.py	100.00% <100.00%> (ø)
trestle/oscal/ssp.py	100.00% <100.00%> (ø)
trestle/oscal/target.py	100.00% <100.00%> (ø)

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[butler54]

LGTM