Add $ delimiter to MathJax config / allow custom MathJax config

[LnLcFlx]

Is your feature request related to a problem? Please describe.
Sites using $tex here$ delimiters for LaTeX equations are not rendered using MathJax.
This is probably due to the default MathJax config that only supports \(tex here\) delimiters.
This can be observed on sites like quantamagazine.org (note here it is technically $latex tex here$ but still...).

Describe the solution you'd like
I suggest either $ is added to the MathJax config as a valid delimiter or, if this would cause trouble with the dollar sign, add some way of configuring this if needed.
And if not in the UI maybe via env variables or a config dir.

Describe alternatives you've considered
A workaround is adding the following lines to the respective site-config (i.e. /var/www/wallabag/vendor/j0k3r/graby-site-config/quantamagazine.org.txt)

find_string: $
#find_string: $latex 
replace_string: \(
find_string: $
replace_string: \)

Additional context
As a global workaround: Is it possible to edit some files in the docker container to change the MathJax config right now?

Related to #5836

[LnLcFlx]

Another totally different thing is to remove MathJax altogether in favor of KaTeX for performance reasons.