add option to disable inline formulas in markdown

[borkdude]

Allow setting {:nextjournal.clerk/markdown {:disable-inline-formulas true}} as ns metadata to disable markdown parsing of $-delimited inline formulas. Fixes #775.

[borkdude]

@mk This looks pretty good imo. I will bump markdown in bb and then the tests should work in bb too. Do we need to support markdown config in other places, e.g. via a system property? Or one system property with a clerk config to rule them all?

[mk]

Do we need to support markdown config in other places, e.g. via a system property? Or one system property with a clerk config to rule them all?

I need to think more about this. Would leave this pr to only add the notebook metadata. We can start collecting use cases for a global clerk config in an issue and then think about how to solve it separately.

[borkdude]

We can start collecting use cases for a global clerk config in an issue and then think about how to solve it separately.

We probably don't even need an issue, we can wait for people to create one after they want more than just the notebook annotation.

Restricting to just notebook metadata for now sounds good.