phosphor-health-monitor: add new D-Bus interface

This commit introduces following changes -
- A new Metrics Value Interface.
- An interface to reset the metrics, if needed.
- Common Threshold interface so it can be used in Metrics and Sensors.

For more detail, please refer to design -
https://gerrit.openbmc.org/c/openbmc/docs/+/64917

Unit Test: meson build passes.

Change-Id: I014a047f9db6fe470124baa41dcce93caf7ceb4b
Signed-off-by: Jagpal Singh Gill <paligill@gmail.com>
diff --git a/gen/xyz/openbmc_project/meson.build b/gen/xyz/openbmc_project/meson.build
index f03b941..573a389 100644
--- a/gen/xyz/openbmc_project/meson.build
+++ b/gen/xyz/openbmc_project/meson.build
@@ -88,6 +88,7 @@
 subdir('Logging')
 subdir('MCTP')
 subdir('Memory')
+subdir('Metrics')
 subdir('Network')
 subdir('Nvme')
 subdir('Object')