Fix/eng 92 cli agent statelink mechanics

[evilsocket]

Closes ENG-92:

• Added a more explicit error message when dreadnode agent push raises a 404 due to a different server profile.
• Added a new profile sub field to links in order to preemptively check this condition and present a meaningful error message.
• Aligned unit tests to these changes.

[linear]

ENG-92 CLI - Agent state/link mechanics

A few general situations we might want to explore for agent management:

• If we have an existing agent folder prepped with a .dreadnode.yaml, and we try to run agent push against a different server (or a reset local server), we just get 404 on creating the version without great feedback to a user. We might want to catch this, and prompt the user to create the agent again.
• I'm not sure how far we've gone down handling a configured .dreadnode.yaml file in an agent when it comes to switching profiles, potentially pushing it to different servers, or using it for different strikes as well. I believe we have the links field for this, but we don't store any type of profile or server url in there.

In general, I think we have some of this logic built, but I'm not sure we've wired everything up for all the situations a user might find themselves in when it comes to context switching an agent between servers, strikes, etc.

[monoxgas]

All looks awesome!