Add option for target name to be used as the MQTT topic

[arychj]

Intent

Adds an optional parameter to the MQTT configuration to use the target's name as the second topic level rather than the hostname.

Example

# config.yml

mqtt:
  # < snip >
  target_name_as_topic: true

targets:
  - host: 192.168.8.81
    name: UPS 3301
    version: 1
    sensors:
      - oid: 1.3.6.1.4.1.3808.1.1.1.1.1.1.0
        name: Model Number

Effect

• before setting target_name_as_topic: messages are published to .../192.168.8.81/...
• after setting target_name_as_topic: messages are published to .../ups_3301/...