Add Katex Equation rendering plugin to Markdown Editor

[guerler]

This PR adds KaTeX support for rendering inline and block equations in the markdown editor. Moving forward, we intend to support inline rendering plugins across more Galaxy markdown components. This PR demonstrates that approach using the markdown-it plugin interface for KaTeX.

Insert in markdown section:

Added new templates:

How to test the changes?

(Select all options that apply)

• I've included appropriate automated tests.
• This is a refactoring of components with existing test coverage.
• Instructions for manual testing are as follows:
  1. [add testing steps and prerequisites here if you didn't write automated tests covering all your changes]

License

• I agree to license these and all my past contributions to the core galaxy codebase under the MIT license.

[mvdbeek]

Can you resolve the conflict ?