Atomic Red Team support in threatest

[juliendoutre]

What does this PR do?

Add support for Atomic Red Team into threatest.

Motivation

Atomic Red team supports multiple host based attacks that are often simply bash commands.

This PR proposes to extend the local and remote detonators configurations to support atomic red team in addition to arbitrary commands.

Remaining questions

• Use an external lib like https://github.com/activeshadow/go-atomicredteam to parse and execute the YAML configuration or use something in-house?
• Embed all atomic test cases in the threatest binary or download them when needed from their github repository?

Checklist

• Unit tests
• Documentation