Upgrade to Vue 3

[kinow]

At the moment the only blocker for Vue 3, I think, is Bootstrap Vue that hasn't upgraded to Vue 3 yet.

bootstrap-vue/bootstrap-vue#5196

The same happened to me in Cylc UI, where we adopted Vuetify. But Jena UI is a much smaller and simpler app, so I'm thinking in doing the following:

• Finish the e2e tests https://issues.apache.org/jira/browse/JENA-2307
• Start re-writing whatever Bootstrap Vue features we use as simple Vue components
• Instead of using bootstrap-vue, use simply bootstrap

That should prevent us from being locked in a version until another library upgrades to Vue 4, 5, etc. Furthermore, using plain Bootstrap makes it easy too in case we someday have to move to React/Angular/Svete/etc (as we did from Backbone → Vue.)

[kinow]

Oh snap. Me and my bad memory. Sorry @afs, ended up duplicating it in #1306. I will close this one since I updated the other issue 👍 Good catch.