Add command to ping services / Pi's

[Agent-E11]

This should take security into account. Using os.system(f"ping -c 1 {service}") to ping a service would be insecure (e.g. someone could make service be google; sudo rm -rf /)

In this case, I think subprocess.run(["ping", "-c", "1", service]) would be more secure

[Agent-E11]

Related to #1, and #6, because it might be a good idea to make a command that creates new services to ping, and only "bot moderators" should be able to use it

[Agent-E11]

There also could be a healthcheck option. Which pings all services, and gives a report

[Agent-E11]

Or, instead of a healthcheck command, there could be a /ping group command which pings all services that are part of a group, and each service has an optional list of groups that it is part of (all services are part of the all group). For instance:

# config.yaml

# ...

services:
  google:
    address: google.com
    groups:
      - external
  pi1:
    address: 192.168.0.201
    groups:
      - internal
      - pi-cluster  
  pi1:
    address: 192.168.0.202
    groups:
      - internal
      - pi-cluster
  vm-server:
    address: 192.168.0.200
    groups:
      - internal

---

/ping group external

pinging services: google

/ping group internal

pinging services: pi1, pi2, vm-server

/ping group pi-cluster

pinging services: pi1, pi2