Migrate to Vue 3

[juliusknorr]

Steps might need to be refined:

• Come up with an overview of dependencies and their vue3 compatibility - which ones we can keep, which are incompatible, needs replacement
• Migration steps that are possible to do before upgrading
• do another stable release and branch off
• Upgrade packages to vue3 and do changes that have not been possible before

Further reference

• Migration to Vue 3 standards#13
• https://v3-migration.vuejs.org/
• https://github.com/nextcloud-gmbh/office-team/issues/47

PR list

• remove deprecated nextcloud-vue-collections #6664

[juliusknorr]

Added a PR list to the first post @grnd-alt