calculate agent alive/dead status server-side

[uruwhy]

Description

• Have the server determine the agent status (alive vs dead vs pending kill) rather than calculate it browser-side as part of the GUI. This eliminates issues where an agent is marked dead due to different time zones or time drift between the c2 server and the user's browser
• add API endpoint to kill agent via POST request to /api/v2/agents/kill/{paw}

Requires mitre/magma#83

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Unit tests, ran with agents and updated magma plugin

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud