Automatable agent update

[foxcpp]

Here I propose a solution to agent updates problem. As we know, it's kinda problematic to replace running binaries on Windows. So there should be some way to update agent "from outside". Here is my plan:

• [x] Add endpoint with agent binary.
• [x] Add updater service.

How it would work

1. Agent launches updater service
2. Updater service stops agent service
3. Updater service downloads agent binary from endpoint mentioned above
4. Updater service replaces old agent binary (so it should have admin access to system)
5. Updater service launches agent back

CC @Hexawolf @leha-bot

[foxcpp]

Is it really a problem? You run net start agent-updater from agent. net start agent-updater of course doesn't starts the service itself, it will only tells Windows to start it. Agent will not even see updater binary.