Un-revert docs site changes that broke deployments

[ptgott]

On Aug 14, 2023, we merged two gravitational/docs PRs:

• 369

• 367

After merging, docs site deployments failed with the following message:

server/rehype-hljs-var.ts(165,42): error TS2345: Argument of type 'MdxJsxFlowElement \| Element' is not assignable to parameter of type 'Content'.
--
13:20:01.677 | Type 'MdxJsxFlowElement' is not assignable to type 'Content'.
13:20:01.677 | Type 'MdxJsxFlowElement' is not assignable to type 'MdxJsxFlowElementHast'.
13:20:01.677 | Types of property 'children' are incompatible.
13:20:01.677 | Type '(BlockContent \| DefinitionContent)[]' is not assignable to type 'ElementContent[]'.
13:20:01.678 | Type 'BlockContent \| DefinitionContent' is not assignable to type 'ElementContent'.
13:20:01.678 | Type 'Code' is not assignable to type 'ElementContent'.
13:20:01.678 | Type 'Code' is not assignable to type 'Raw'.
13:20:01.678 | Types of property 'type' are incompatible.
13:20:01.678 | Type '"code"' is not assignable to type '"raw"'.
13:20:01.719 | error Command failed with exit code 1.

This also affected the docs linter in gravitational/teleport CI workflows.

Let's do this:

• [ ] Investigate the cause of the error and why it evaded CI
• [ ] Find a way to prevent similar errors from slipping past CI in the future
• [ ] Un-revert the two PRs we reverted