[Enhancement] Ability to add mathematical formulas in features description

[malekadrar]

Right now I don't think that we can add mathematical formulas in features description. For example, it's not possible to get this:

The solution I found is very simple which I would like to share with you, using MathJax. To do so, I've add the following new file math.ftl under serenity-core\serenity-report-resources\src\main\resources\freemarker\libraries directory and here is his content:

   <!-- mathjax -->
  <script src="https://polyfill.io/v3/polyfill.min.js?features=es6"></script>
  <script id="MathJax-script" async src="https://cdn.jsdelivr.net/npm/mathjax@3.0.1/es5/tex-mml-chtml.js"></script>

And I only included it in the file requirements.ftl under serenity-core\serenity-report-resources\src\main\resources\freemarker directory like this:

    <#include "libraries/math.ftl">

and compiled the library.

After that it's possible to use the LaTeX language. For instance, to get the above result, here is the feature description:

    Feature: The zeros of a second-degree polynomial
    
    If \\(a \ne 0\\) and \\(\(b^2-4ac\) \ge 0\\), there are two solutions to \\(ax^2 + bx + c = 0\\) and they are \\[x = {-b \pm \sqrt{b^2-4ac} \over 2a}.\\]
    
    **Euler formula**
    
    \\[
        \sum_{n=1}^{+\infty} \frac{1}{n^2} = \frac{\pi^2}{6}
    \\]

          Scenario: ...
                Given ...
                When ...
                Then ...

Of course it's possible to combine MathJax with the Markdown.

Originally posted by @malekadrar in #3070

[wakaleo]

Can you propose a PR for this?