Replace paths, so they are equal on every OS

[Zeegaan]

Notes

• Fixes an issue, where you could not get the logos on windows.
  This was because of the newly introduced Explicit endpoints returning the Login and BackOffice logos and background #17696. Which uses Path.Combine, which in turn on windows, combines paths with \, but all our static paths are /.
  • Note: The jumbled path works with Physical Files, but as when we ship this, its in an RCL, it does not work with that.
• This PR remedies that by just not using Path.Combine, and instead just having the / in there always

How to test

• Run the backoffice, you should still see the Logos
• You can also pack the project, and run the template to make sure its still there.

[nikolajlauridsen]

Looks good tests good 👍