feat: migrate to vue 3

[st3iny]

Ultra early WIP

Resolves #712

Requires

• [x] https://github.com/nextcloud-libraries/nextcloud-dialogs/pull/884 (+ some unpushed patches)
• [x] https://github.com/nextcloud-libraries/webpack-vue-config/pull/331 (imported via github:*)
• [x] https://github.com/nextcloud-libraries/nextcloud-password-confirmation/pull/967

TODO

• [x] Migrate settings entry point
• [x] Migrate challenge entry point
• [x] Migrate login-setup entry point
• [x] Fix tests (probably)
• [ ] Wait for release of @nextcloud/password-confirmation