Fix latex errors in documentation

[gassmoeller]

This should go a big step towards resolving the first task in #6178 and make our documentation compile in the pdf mode of Sphinx.

Fixes in this PR:

• We used to escape some constructs in the parameter documentation like [x,y](z) for the markdown documentation, because they look like markdown links, unfortunately we changed them to \[x,y\](z). However \[ and \] start and end math mode in Latex, which broke the Latex build. So I now replace [x,y](z) with {x,y}(z) inside the parameter documentation instead.
• References in figure captions broke the tex file, because the \hyperlink command inside a \caption wouldnt work as reported here: https://tex.stackexchange.com/questions/522524/using-hyperrefs-hyperlink-command-inside-caption-in-figure-environment. I took some inspiration from Latex issue when is included a citation in the caption of a table or figure mcmtroffaes/sphinxcontrib-bibtex#276 to work around the issue (redefining the \hyperlink macro to always be \protect\hyperlink, maybe a bit drastic, but it seems to work)
• adding the siunitx package again into the generated tex file. With some trickery we may be able to get all the \si commands to work at least in the .pdf manual
• add cairosvg into the environment file of the documentation (I think this was just not done in sphinx doc: add plugin for svg conversion #6181 because it was probably already installed on that test machine)
• unified the name of a parameter (\viscosity is not valid latex, \eta is)
• the last change also made it necessary to update the parameter files, so I ran update_parameters.sh

I can now run make latexpdf successfully locally, let's see what readthedocs says.

[tjhei]

Awesome, thank you.