update machine-api-usage-telemetry

During implementation of this enhancement we have determined that there
will be a need for two labels on the MachineHealthCheck related
metrics. Although these labels have unbounded cardinality, it will only
need to be exported through telemetry as a sum without the need for the
labels.

enhancements/machine-api/machine-api-usage-telemetry.md

@@ -259,11 +259,14 @@ will need to be exposed through telemetry. These metrics are:
     * This should be exported through the `cluster:usage:resources:sum` series with
     a resource type of `machinehealthchecks.machine.openshift.io`.
 * MachineHealthCheck total nodes covered count
-    * `mapi_machinehealthcheck_nodes_covered` - This metric has no labels.
+    * `mapi_machinehealthcheck_nodes_covered` - This metric has two labels representing
+    the name and namespace of the machine health check.
 * MachineHealthCheck successful remediations count
-    * `mapi_machinehealthcheck_remediation_success_total` - This metric has no labels.
+    * `mapi_machinehealthcheck_remediation_success_total` - This metric has two labels
+    representing the name and namespace of the machine health check.
 * MachineHealthCheck short circuit state
-    * `mapi_machinehealthcheck_short_circuit` - This metric has no labels.
+    * `mapi_machinehealthcheck_short_circuit` - This metric has two labels representing
+    the name and namespace of the machine health check.
 
 **Metric series to be exported**
 
@@ -275,8 +278,8 @@ will need to be exposed through telemetry. These metrics are:
   with no labels.
 * Total MachineAutoscaler resource count, using `cluster:usage:resources:sum{resource="machineautoscalers.autoscaling.openshift.io"}`.
 * Total MachineHealthCheck resource count, using `cluster:usage:resources:sum{resource="machinehealthchecks.machine.openshift.io"}`.
-* Total nodes covered by MachineHealthChecks count, using `mapi_machinehealthcheck_nodes_covered` with no labels.
-* Total remediations completed by MachineHealthChecks count, using `mapi_machinehealthcheck_remediation_success_total` with no labels.
+* Total nodes covered by MachineHealthChecks count, using a sum of all `mapi_machinehealthcheck_nodes_covered` with no labels on the series.
+* Total remediations completed by MachineHealthChecks count, using a sum of all `mapi_machinehealthcheck_remediation_success_total` with no labels on the series.
 
 In addition to the metrics defined above, the alerts generated by the Machine
 API components will be used to augment this data. The listings below are