Add endhost and haproxy appliances

[b-ehlers]

Basic appliances for endhost and haproxy.

---

When creating a new appliance:

• It's tested locally, i.e.
  • [x] You dragged an instance into a project on your box, got it installed (if necessary), and did some basic network checks (ping, UI reachable, etc.).
  • [x] GNS3 VM can run it without any tweaks.
  • [x] The device is in the right category: router, switch, guest (hosts), firewall
  • [x] You filled in as much info as possible (checks the schemas and other appliance files for some guidance).
• [x] When adding a container: it builds on Docker Hub and can be pulled.
• [ ] The filenames in the "images" section are unique (to avoid appliances and/or versions overwriting each other).
• [x] If you forked the repo, running check.py doesn't drop any errors for the new file.
• [ ] Optional: a symbol has been created for the new appliance.