feat(SimpleVM): Reference to new wiki

[vktrrdk]

@dweinholz

When trying to test, you need the latest mkdocs-webhook version, as we now use the macros-plugin

needs SIMPLEVM_WIKI_LINK environment-variable, which will set the link on the page referencing to the new wiki
defaults to https://simplevm.denbi.de/wiki/

Portal-PR: https://github.com/deNBI/cloud-portal/pull/2246

Try to fulfill the following points before the Pull Request is merged:

• Please create your prs against the dev branch
• Please WAIT for the tests to finish.
• All tests have been successfully completed.
• When adding a new documentation or tutorial, make sure that the markdown is linked in the config.yml