FE: Show alerts tab

Why are we doing this work

• the threat monitoring alerts show show up in a separate tab on the Security & Compliance -> Threat Monitoring page

Design

• https://www.youtube.com/watch?v=HuZgaMKdJF0&feature=youtu.be

Implementation plan

• backend allow for the threat_monitoring_alerts feature flag to be accessible in the frontend
• frontend create a new tab for alerts that displays an empty div