Update to Vue.js 3

[Vue 2 has reached End of Life on December 31st, 2023](https://v2.vuejs.org/eol/) and must be replaced by Vue.js 3. `@vue/compat` may be required for bootstrap-vue 2, as neither [bootstrap-vue 3](https://bootstrap-vue.org/vue3) nor [BootstrapVueNext](https://bootstrap-vue-next.github.io/bootstrap-vue-next/docs.html) are ready yet.