Port to Vue 3

[TheKodeToad]

Vue 2 has been EOL for over a year

• Switched to vue3-highlightjs as @highlightjs/vue-plugin does not support v-highlightjs directive
• For some reason languages don't need to be registered any more and I have no idea why
• Switching tabs in docs unhighlights the plugin. This seems to be a vue-router bug: Active class not applied on RouterLink when using to with string or object with path key vuejs/router#2419. it could possibly be worked around with a custom component
• This is my first time working with vue 😆
• No need for fix(docs): hljs deprecations and new directive #471 if this is merged

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[cla-bot]

Thank you for contributing to Zeppelin! We require contributors to sign our Contributor License Agreement (CLA). To let us review and merge your code, please visit https://github.com/ZeppelinBot/CLA to sign the CLA!

[cla-bot]

Thank you for contributing to Zeppelin! We require contributors to sign our Contributor License Agreement (CLA). To let us review and merge your code, please visit https://github.com/ZeppelinBot/CLA to sign the CLA!

[cla-bot]

Thank you for contributing to Zeppelin! We require contributors to sign our Contributor License Agreement (CLA). To let us review and merge your code, please visit https://github.com/ZeppelinBot/CLA to sign the CLA!

[TheKodeToad]

I think it's in good enough a state to be reviewed.