[mdatagen] Add variable for metric name (#12531)

<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
#### Description
Add variable for metric name in mdatagen, accessing via
`metadata.MetricsInfo.<metric-variable>.Name`

<!-- Issue number if applicable -->
#### Link to tracking issue
Fixes #12459 

<!--Describe what testing was performed and which tests were added.-->
#### Testing
n/a

<!--Describe the documentation added.-->
#### Documentation
Added

<!--Please delete paragraphs that you did not use before submitting.-->

Author: sincejune

.chloggen/add-metric-name-variable.yaml

@@ -0,0 +1,25 @@
+# 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. otlpreceiver)
+component: mdatagen
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Add variable for metric name in mdatagen
+
+# One or more tracking issues or pull requests related to the change
+issues: [12459]
+
+# (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: Access metric name via `metadata.MetricsInfo.<metric-variable>.Name`
+
+# 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: [api]

cmd/mdatagen/internal/sampleconnector/internal/metadata/generated_metrics.go

@@ -56,6 +56,24 @@ var MapAttribute{{ $name.Render }} = map[string]Attribute{{ $name.Render }}{
 {{ end }}
 {{- end }}
 
+var MetricsInfo = metricsInfo{
+    {{- range $name, $metric := .Metrics }}
+    {{ $name.Render }}: metricInfo{
+        Name: "{{ $name }}",
+    },
+    {{- end }}
+}
+
+type metricsInfo struct {
+	{{- range $name, $metric := .Metrics }}
+	{{ $name.Render }} metricInfo
+	{{- end }}
+}
+
+type metricInfo struct {
+    Name string
+}
+
 {{ range $name, $metric := .Metrics -}}
 type metric{{ $name.Render }} struct {
 	data     pmetric.Metric // data buffer for generated metric.