Use API to kill agent, fetch agent status from server

[uruwhy]

Description

• Use the new POST /api/v2/agents/kill/{paw} endpoint to kill agents
• Don't calculate agent status via browser side, rather get it from the server itself

Requires mitre/caldera#3249

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?

Ran agents, tested killing them and letting them time out

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