Update the App.vue to show a basic Greensight dashboard structure

[AMorgaut]

Is your feature request related to a problem? Please describe.

The main application page is currently just the default view generated by the npm create vue@latest command

Describe the solution you'd like

This page should show at least a basic Ecocode Dashboard interface

In the contexte of the Ecocode Challenge, 2 branches will be associated to this feature request

• a "POC" branch trying to copy/paste the greensight Vue.js application and make it run almost as-is
  • Warning - it is not meant to be marged but to be used for demo and analyses
• a "Clean" branch trying to recreate similar page structure rendering
  • Warning - the goal is not to have the dashboard wigets working to have the main structure and "potentielly" very basic component view with no or static data