Resolve "Remove YAML front matter from editable content in the Static Site Editor"

What does this MR do?

Adds the initial abstraction such that subsequent MRs can properly parse out frontmatter and content from a source file. This is needed as there are two modes in which editing is to occur (markdown and WYSIWYG), but we only want the content (not the frontmatter) to display in the WYSIWYG mode.

This is planned MR 1 of 3

Screenshots

N/A

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done