add health_metric_config implementation

Add the health_metric_config interface and implementation for
phosphor-health-monitor. This interface will be used in the
re-write of phosphor-health-monitor.
This change is in relation to following design and D-Bus interface
update-
https://gerrit.openbmc.org/c/openbmc/docs/+/64917
https://gerrit.openbmc.org/c/openbmc/phosphor-dbus-interfaces/+/64914

gtest added for UT.

Change-Id: Ic40faafbb57597023cc70036428d46ee69a895a2
Signed-off-by: Jagpal Singh Gill <paligill@gmail.com>
diff --git a/meson.options b/meson.options
new file mode 100644
index 0000000..0fc2767
--- /dev/null
+++ b/meson.options
@@ -0,0 +1 @@
+option('tests', type: 'feature', description: 'Build tests')