fix the problems with project sharing

[josihoppe]

• add decorator to use in views instead of repeating checks for user / viewer
• check the problems described in:
  • Issue 464
  • this comment
• adjust sharing rights for these problems

[paulapreuss]

@josihoppe Code looks nice, thanks for this refactoring! I think it will really improve maintenance regarding this topic ✨

I tested around a bit sharing with myself and I noticed the following:

• If I have a project with read rights, I can still update the parameters on the assets in the energy system (asset_create_or_update). Once I do that, I am also able to restart the simulation. If there is no simulation on the scenario yet, I am also able to start a simulation. I only get a 403 if I try to reset the existing simulation with no parameters changed. That shouldn't be possibe just with read rights.
• If a project is shared with me (both for edit and read rights), I do not see the button for project deletion, so I can't actually remove the project again from the projects view, although in the backend now it should work to just revoke the access.

After these things are fixed, I will rebase on main and hopefully have fixed the build dependencies and update the changelog before we merge.