Feature: Enable reference style links

[jcalcaben]

Description

Updates the gatsby-plugin-mdx dependency to 2.5.0, which contains my reference style link bugfix (gatsbyjs/gatsby#30967).

Related Issue

Closes #305

Motivation and Context

Enables reference-style links for documentation projects that currently or may use it.

How Has This Been Tested?

1. Converted an inline link in the root index.md page into a reference style link.
2. Created a production build with prefix and pointed the HTTP server to the build artifacts: yarn start:prefix
3. Navigated to http://localhost:9000/example/
4. Verified the contributing page link destination contains the example base URL

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have signed the Adobe Open Source CLA.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.