[mqtt.homeassistant] Include the details of JSON syntax errors when p…

…arsing fails

While it's useful in general to not have to copy/paste a MQTT message into a JSON
parser to verify syntax, it also includes details about fields that are the wrong
data type that a generic JSON parser won't catch. A la openhab#17375.

bundles/org.openhab.binding.mqtt.homeassistant/src/main/java/org/openhab/binding/mqtt/homeassistant/internal/config/dto/AbstractChannelConfiguration.java

@@ -226,7 +226,7 @@ public static <C extends AbstractChannelConfiguration> C fromString(final String
  }
  return config;
  } catch (JsonSyntaxException e) {
- throw new ConfigurationException("Cannot parse channel configuration JSON", e);
+ throw new ConfigurationException("Cannot parse channel configuration JSON: " + e.getMessage(), e);
  }
  }
 }