Let the Checkmate Capture agent push data to the Hub

**Is your feature request related to a problem? Please describe.**

Sometimes, it's a hassle to open the port for the capture agent or you don't have a static ip address to configure. Both would be typical for example in a scenario when you want to monitor a server at your home. I guess there are many other occasions where this could happen, for example in with kubernetes where you would have much configuration to do.

**Describe the solution you'd like**

Make it possible to configure an capture agent to start the communication with the Checkmate Hub API.
The agent would also need to pull its config from the hub (like: "report every 15 seconds"). With this, it can send the same stats it delivers now on get requets with posts to the hub.

A gratis perk is that the sent data is probably encrypted, because it likely that the hub is running on https, rather then an agent on a system that has not already an infrastructure for serving SSL.

**Describe alternatives you've considered**

In most situations this would only be convenience feature, so this is not a showstopper anywhere i guess.

Additionally, this could generate a shadow IT in edge cases, e.g. in classic development agencies, because a developer doesn't have to talk to OPS people to open ports.

Start by locating the capture agent and the Checkmate Hub API, then trace the existing GET-based stats flow. Review how agent configuration such as the reporting interval is currently provided. Done means defining and implementing the agent-initiated communication and configuration flow, with coverage for posting the existing stats.

Written by the indexing model from the issue text.