Implemented enhancements:
- [Feature Request] Add alert observable API endpoints #1732
- [Feature Request] Add alert import date property #1733
- [Feature Request] Add handling duration properties to imported Alert type #1734
Fixed bugs:
- [Bug] TheHive doesn't start if cassandra is not ready #1725
- [Bug] Alert imported multiple times (bis) #1738
- [Bug] Cosmetic fix in alert observables list #1744
