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/yaml/xyz/openbmc_project/Metrics/Value.interface.yaml b/yaml/xyz/openbmc_project/Metrics/Value.interface.yaml
new file mode 100644
index 0000000..e0d6441
--- /dev/null
+++ b/yaml/xyz/openbmc_project/Metrics/Value.interface.yaml
@@ -0,0 +1,57 @@
+description: >
+    This interface provides the Board Manager Metric values for resource
+    utilization.
+
+properties:
+    - name: Value
+      type: double
+      description: >
+          The current metric value.
+      flags:
+          - readonly
+    - name: MaxValue
+      type: double
+      default: infinity
+      flags:
+          - readonly
+      description: >
+          The maximum supported metric value.
+    - name: MinValue
+      type: double
+      default: -infinity
+      flags:
+          - readonly
+      description: >
+          The minimum supported metric value.
+    - name: Unit
+      type: enum[self.Unit]
+      description: >
+          The unit for metric value. For example, memory in bytes, CPU in
+          percent, reboots in count.
+      flags:
+          - const
+
+enumerations:
+    - name: Unit
+      description: >
+          Metric value unit.
+      values:
+          - name: Bytes
+            description: >
+                Unit to indicate bytes.
+          - name: Count
+            description: >
+                Unit to indicate counts.
+          - name: Percent
+            description: >
+                Unit to indicate percentage.
+
+associations:
+    - name: measuring
+      description: >
+          Metrics measure the inventory item's resource utilization, therefore
+          implement an association to the inventory item.
+      reverse_names:
+          - measured_by
+      required_endpoint_interfaces:
+          - xyz.openbmc_project.Inventory.Item