KPI for client

[Xantass]

Describe your changes

add new route for get all KPI for POS or KDS

How to test the feature

call the route 'displayKpi' and check the data return

Issue ticket number and link

Closes #172

Checklist before requesting a review

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have performed a self-review of my code
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Documentation has been updated as required
  If a single item in this checklist is not checked, the pull request cannot be accepted

[JulesGresset]

Globaly works but some issues :

• averagePrepTime and averageWaitingTime are inverted in both KDS and POS
• clientsCount does not work in both KDS and POS
• ordersInProgress in POS doesnt works
• Some console.log still here