Add helper to have the links open as external pages

This MR solves a problem that links like "www.gfz-potsdam.de" are not opened as "https://www.gfz-potsdam.de" but instead as "sensors.gfz-potsdam.de/www.gfz-potsdam.de".

For some of the links (mostly the attachments and the repository urls for the update actions) we enforce to have the http(s):// prefix. For the websites for devices, platforms, sites and contacts we didn't enforced that in the past.

So that there is the option that we have problems with it, we need this wrapper here, so that the links can be opened as they should.