Adds extension for mkdocs admonition.

[jvanderaa]

Closes: #362

What's Changed

• Adds an extension to complete admonitions.

To Do

• [x] Explanation of Change(s)
• [x] Added change log fragment(s) (for more information see the documentation)
• [x] Attached Screenshots, Payload Example
• [x] Unit, Integration Tests
• [x] Documentation Updates (when adding/changing features)
• [x] Outline Remaining Work, Constraints from Design