Improve Alert Proximity When Previewing

[saadkadhi]

Request Type

Feature Request

Work Environment

Question	Answer
TheHive version / git hash	2.13.2

Problem Description

When previewing alerts, TheHive shows their proximity with existing cases by showing the number of shared observables and IOCs. This is not good but not enough to make an informed decision on whether to import or not an alert and if so whether to add it to an existing case or not.

Possible Solutions

When #365 is implemented, add the number of observables in the alert that correspond to sighted IOCs in existing cases as well to further the analyst make a decision.