[receiver/vcenter] Fix datastore disk usage metric (open-telemetry#23654

)

**Description:** 
Fixed a bug in which the Vcenter receiver was incorrectly emmiting the
disk_state: used datapoint twice under the vcenter.datastore.disk.usage
metric instead of a
disk_state: used
disk_state: available

**Documentation:** <Describe the documentation added.>

.chloggen/fix-incorrect-diskusage-metric-emission.yaml

@@ -0,0 +1,20 @@
+# Use this changelog template to create an entry for release notes.
+# If your change doesn't affect end users, such as a test fix or a tooling change,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: bug_fix
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: vcenterreceiver
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Fixed a bug in which the vCenter receiver was incorrectly emitting the "used" attribute twice under the vcenter.datastore.disk.usage metric instead of "used" and "available".
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [23654]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:

receiver/vcenterreceiver/metrics.go

@@ -103,7 +103,7 @@ func (v *vcenterMetricScraper) recordDatastoreProperties(
 	diskUsage := s.Capacity - s.FreeSpace
 	diskUtilization := float64(diskUsage) / float64(s.Capacity) * 100
 	v.mb.RecordVcenterDatastoreDiskUsageDataPoint(now, diskUsage, metadata.AttributeDiskStateUsed)
-	v.mb.RecordVcenterDatastoreDiskUsageDataPoint(now, s.Capacity, metadata.AttributeDiskStateUsed)
+	v.mb.RecordVcenterDatastoreDiskUsageDataPoint(now, s.FreeSpace, metadata.AttributeDiskStateAvailable)
 	v.mb.RecordVcenterDatastoreDiskUtilizationDataPoint(now, diskUtilization)
 }
 

receiver/vcenterreceiver/testdata/integration/expected.yaml

@@ -166,7 +166,7 @@ resourceMetrics:
                   attributes:
                     - key: disk_state
                       value:
-                        stringValue: used
+                        stringValue: available
                   startTimeUnixNano: "1682367880520917116"
                   timeUnixNano: "1682367880570405002"
             unit: By