Strip HTML out of python decision point values when rendering decision points to json

[ahouseholder]

This issue could be made redunant by a solution to

• Revise Safety decision point value text #482

Otherwise, at present, we have HTML content in the description of the Safety decision point following the merge of #479. The end result, as described in that PR

• make safety table formats look better #479

is that the JSON file emitted contains that HTML markup, and it really should not.

One approach would be to add a wrapper method on the SsvcDecisionPointValue class in src/ssvc/decision_points/base.py to strip out HTML from the description field when calling the to_json method provided by the dataclass_json decorator.

Another approach could be to override the encoder for _Base.description in src/ssvc/_mixins.py. See for example https://pypi.org/project/dataclasses-json/#Overriding