Implement chart to display stats

[tintamarre]

I would be great to display some stats about the API in the frontend.

A URL in Omdat is currently exposed without anything to show (https://omdat.openjustice.lltl.be/statistics*) and the backend API URL is available with a simple GET request as documented,

The short term vision is to show a graph with the number of documents per year and per court over time. The current way to go to display chart in Omdat is to use ApexChart as it is already implemented and in use in Court.vue#L120-L139.

In the long run, it would be great to also show chart of:

• number of documents per type ;
• number of documents per source ;
• number of documents available vs documents produced by court (data still needed but @RRINKIN had a conversation about it with SPF) ;
• etc.