Update API for event pagination on the server side

Pagination is currently performed on the client side. This will become a problem when there will be loads of events for a single investigation because :

• html message sent to the client will become too large, thus reducing the app reactivity
• client computer will need more resource to handle the potential hundred of thousand of events received to be displayed.

Work:

• Modify swagger file documenting the updated API
• Update the API method for getting events for a given investigation
• Create a new API method to GET the total number of events for a given investigation