Initial gray-matter replacement

What does this MR do?

1. Replaces gray-matter with a lighter payload approach (front_matterify.js)
2. Additionally let's us converge on a single js-yaml across the codebase
3. When other front-matter language support becomes needed we can iterate on the solution to dynamically import the target parser (or maybe even offload to the backend?). YAGNI for now as YAML is the core/common target.

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

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Closes #247127 (closed)