Add metric-specific labels in googlecloudmonitoringreceiver component (open-telemetry#35828)

#### Description
Add metric-specific labels inside the googlecloudmonitoringreceiver
component

#### Link to tracking issue

open-telemetry#35711

#### Testing

#### Documentation

Author: abhishek-at-cloudwerx

.chloggen/add-metric-labels-in-googlecloudmonitoringreceiver.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: googlecloudmonitoringreceiver
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Add metric-specific labels to googlecloudmonitoringreceiver component
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [35711]
+
+# (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:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: []

receiver/googlecloudmonitoringreceiver/receiver.go

@@ -271,17 +271,24 @@ func (mr *monitoringReceiver) convertGCPTimeSeriesToMetrics(metrics pmetric.Metr
 		}
 
 		// Set metadata (user and system labels)
-		if timeSeries.Metadata != nil {
-			for k, v := range timeSeries.Metadata.UserLabels {
+		if timeSeries.GetMetadata() != nil {
+			for k, v := range timeSeries.GetMetadata().GetUserLabels() {
 				resource.Attributes().PutStr(k, v)
 			}
-			if timeSeries.Metadata.SystemLabels != nil {
-				for k, v := range timeSeries.Metadata.SystemLabels.Fields {
+			if timeSeries.GetMetadata().GetSystemLabels() != nil {
+				for k, v := range timeSeries.GetMetadata().GetSystemLabels().GetFields() {
 					resource.Attributes().PutStr(k, fmt.Sprintf("%v", v))
 				}
 			}
 		}
 
+		// Add metric-specific labels if they are present
+		if len(timeSeries.GetMetric().Labels) > 0 {
+			for k, v := range timeSeries.GetMetric().GetLabels() {
+				resource.Attributes().PutStr(k, fmt.Sprintf("%v", v))
+			}
+		}
+
 		// Store the newly created ResourceMetrics in the map
 		resourceMetricsMap[resourceKey] = rm
 	}