Move template settings to vue component

[elzody]

• Target version: main

Summary

This resolves the issue on main where we are still using a legacy file upload plugin, causing an error and failing tests. I took the chance to migrate the global template settings to a Vue component, a start which I hope will lead to a cleanup of the admin settings in general, since everything is shoved into one large AdminSettings.vue component, and it's messy and difficult to reason about.

TODO

• [x] add cypress tests

Checklist

• [x] Code is properly formatted
• [x] Sign-off message is added to all commits
• [x] Documentation (manuals or wiki) has been updated or is not required