Vue 3 migration

[mariobalca]

Changes proposed ✍️

• Migrate Vue from version 2.7.8 to version ^3.2.29
• Migrate Vuex from version 3.5.1 to version ^4.0.2
• Migrate VueCLI from version 4.5.6 to version ^5.0.1 (which is now also using Webpack 4)
• Migrate VueRouter from version 3.4.3 to version ^4.0.12
• Migrate TailwindCSS from version ^2.2.16 to ^3.0.22
• Migrate ElementUI to ElementPlus
• Update ESLint configurations to follow Vue 3 recommended settings.

Checklist ✅

• Label appropriately with type:feature 🚀, type:enhancement ✨, type:bug 🐞, or type:documentation 📜.
• Tests are passing.
• New backend functionality has been unit-tested. (not applicable)
• Environment variables have been updated (not applicable)
  • Front-end: frontend/.env.dist
  • Backend: backend/.env.dist, backend/.env.dist.staging, backend/.env.dist.staging.
  • Configuration docs have been updated.
  • Team members only: update environment variables in Password manager and update the team
• API documentation has been updated (if necessary) (see docs on API documentation). (not applicable)
• Quality standards are met.
• All changes have been tested in a staging site.
• All changes are working locally running crowd.dev's Docker local environment.

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