[Feature Request] Add MarkdownContext to BuildOptions.ConfigureMarkdig

**Is your feature request related to a problem? Please describe.**
When creating custom extensions, I want to have access to the markdown context for things like the `getToken` function, which would allow to add translations for the plugins in the `token.json`

**Describe the solution you'd like**
Add a new parameter in `ConfigureMarkdig` Func of type MarkdownContext

**Describe alternatives you've considered**

**Additional context**

Start by locating BuildOptions.ConfigureMarkdig and the MarkdownContext type, then inspect how custom extensions receive configuration. Confirm the intended callback signature and identify related coverage; done when custom extensions can access MarkdownContext through ConfigureMarkdig and the behavior is tested.

Written by the indexing model from the issue text.