Use GitLab Mono over JetBrains Mono

What does this MR do and why?

Use GitLab Mono over JetBrains Mono

This enables us to only ship two font files, disable the ligature hack and fixes the Backtick bug.

Screenshots or screen recordings

Where	Before	After
Inside GitLab
Web IDE	-

tested with:

This **`is bold fff`** _`italic fff`_ and **_`bold italic fff`_** and `normalfff` monospace.

`=>` no ligatures and no Backtick bug:

~~~markdown
`A`
~~~

How to set up and validate locally

1. Edit any markdown and use monospace characters (see above)
2. Because the font is lazy loaded, it could be that you need to reload and the font only loads on 2nd load

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.