Remove deprecated MDX-GFM storybook addon

[maxatdetroit]

Describe the bug

When running storybook, observe the warning about MDX addon deprecation:

WARN The "@storybook/addon-mdx-gfm" addon is meant as a migration assistant for Storybook 7.0; and will likely be removed in a future version.
WARN It's recommended you read this document:
WARN https://storybook.js.org/docs/react/writing-docs/mdx#lack-of-github-flavored-markdown-gfm
WARN
WARN Once you've made the necessary changes, you can remove the addon from your package.json and storybook config.

To Reproduce
Steps to reproduce the behavior:

1. Go to project root
2. Run yarn storybook
3. See warning

Expected behavior

No deprecation warning should appear.

We need to follow the instruction at https://storybook.js.org/docs/writing-docs/mdx#lack-of-github-flavored-markdown-gfm to migrate any GFM styled markdown and remove the addon.