monitor: Support target_path option in configuration file

The target path containing the interface
xyz.openbmc_project.control.FanPwm or
xyz.openbmc_project.control.FanSpeed can be different between
phosphor-hwmon and dbus-sensor.

In phosphor-hwmon, it is "/xyz/openbmc_project/sensors/fan_tach/".
In dbus-sensor, it is "/xyz/openbmc_project/control/fanpwm/".

This commit supports making this path configurable via "target_path"
as a full object path.
By default, it is the same as the fan tach object path.

Signed-off-by: Chau Ly <chaul@amperecomputing.com>
Change-Id: I2658a462dd49a98ad77d684f2927e6ccae21cd15
diff --git a/monitor/example/monitor.yaml b/monitor/example/monitor.yaml
index 8d70c4f..14fce2c 100644
--- a/monitor/example/monitor.yaml
+++ b/monitor/example/monitor.yaml
@@ -28,6 +28,10 @@
 #                  setting a fan speed (otherwise just for reads)]
 #      target_interface [The fan target interface used by the sensor.
 #                        Default is "xyz.openbmc_project.Control.FanSpeed"]
+#      target_path [The full target path, which implements
+#                   xyz.openbmc_project.Control.FanSpeed or
+#                   xyz.openbmc_project.Control.FanPwm interface.
+#                   Default is /xyz/openbmc_project/sensors/fan_tach/*"]
 #      factor [The factor to multiply with target to calculate the expected
 #              fan speed. Default is 1 for fan speed target;
 #              Customized value for pwm target]