regulators: Create SensorMonitoring class

Create C++ class that implements the 'sensor_monitoring' element from
the JSON config file.  See sensor_monitoring.md for more information.

The execute() method of this class will be implemented in a future
commit.

Signed-off-by: Shawn McCarney <shawnmm@us.ibm.com>
Change-Id: Ifd0530e54d71a5292e8f4e5cad0a13195e801ed8
diff --git a/phosphor-regulators/test/meson.build b/phosphor-regulators/test/meson.build
index 38c038d..547529c 100644
--- a/phosphor-regulators/test/meson.build
+++ b/phosphor-regulators/test/meson.build
@@ -12,6 +12,7 @@
     'presence_detection_tests.cpp',
     'rail_tests.cpp',
     'rule_tests.cpp',
+    'sensor_monitoring_tests.cpp',
     'write_verification_error_tests.cpp',
 
     'actions/action_environment_tests.cpp',