[BUG] Homebridge taken offline if Pi-hole is down
**Describe the bug**
I'm doing some work on my NAS which hosts my pi-hole server, and with the pi-hole docker not running I noticed all of my homebridge accessories went offline. When I checked homebridge, it was crashing in a loop. 

I suspected the issue had to do with my NAS being down, and when I changed the IP used for the Pi-hole plugin in homebridge config to something else, homebridge was able to stay online. It seems the server being online, but not responsive causes this issue and using a random non-existant IP does not.

I have logging set to info level, but all I ever see is:
`[12/7/2021, 5:49:15 PM] [Pihole] Initializing Pihole accessory...`

**To Reproduce**
Steps to reproduce the behavior:
1. Create a pi-hole server running pi-hole in docker
2. Setup Homebridge plugin to have 5 minute off switch for pi-hole (nothing special, no child bridge)
3. Verify pi-hole and homebridge setup work as expected
4. Close docker, keeping the server IP online
5. Check homebridge

**Expected behavior**
Pi-hole plugin should be able to handle communication issues without bringing down Homebridge.

**Desktop (please complete the following information):**
 - OS: macOS 21C5045a running Homebridge v1.3.8
 - Browser: Safari
 - Version: homebridge-pihole v0.3.5