Use HTML in JsonPropertyDescription instead of Markdown

[dlvenable]

Is your feature request related to a problem? Please describe.

Data Prepper now produces schemas with property descriptions.

These are currently using Markdown because that is what we used on the documentation website. But, this can be useful for other tools. Some tools support reading HTML directly, but not Markdown.

Describe the solution you'd like

Use HTML in the property descriptions rather than Markdown to support more systems.