Update markdown description handling

[bourdakos1]

The goal of this PR is to generate a single markdown file for all static content. This will enable richer features for markdown descriptions and potential flexibility to allow users to supply their own markdown generator. This should also remove the react-markdown dependency as well as hardcoded remark/rehype plugins.

TODO:

• Update docMetadata/versionsMetadata to apiMetadata
• currentDocRoute -> currentApiRoute
• sidebarName should come from the plugin and be unique
• Metadata should include className for html tag (this was for versioned docs which is unneeded for our use case)
• ApiItem shouldn't use docusaurus context
• We should add a way to supply keywords and image to SEO
• Ensure all PluginOptions are hooked up and work as expected
• Update table margin styles