[docs] moving Parser Docs to new index

[paulOsinski]

This PR moves the parser documentation to a new URL index https://docs.defectdojo.com/en/connecting_your_tools/parsers/ => https://docs.defectdojo.com/supported_tools to clean things up.

Primarily intended to make the documentation more navigable, because our list of parsers overflows the screen when it's expanded from the main documentation. This moves things into a more walled-off 'appendix' like section while keeping the navigation the same.

Primarily affects the nav - left side is the new version, right side is the old (where Parser docs are mashed in with everything else).

• merged with "hugoupdate" branch so that I could preview the changes.
  [sc-11972]

[valentijnscholten]

The unit tests need an update as they expect the docs to be in a certain folder.

[paulOsinski]

@valentijnscholten I believe I've sorted this out here but I haven't been able to run the unittests locally yet.