Support FrontMatter for codex processor

[mgan59]

Context

We would like to add support for front-matter yaml inside of the top of markdown documents

Actions

There is a plugin/transform called remark-frontmatter that provides an interface with remark().

Integration should consist of the following:

• Add the package to our dependencies
• Update the process() wrapper function with the interface
• May need to do some magic for ESM Support
• Update tests with new case or assertion(s)