[chore] use mdatagen for processorhelper (#10122)

This updates the processor helper to use mdatagen for its internal
telemetry.

---------

Signed-off-by: Alex Boten <223565+codeboten@users.noreply.github.com>

processor/go.mod

@@ -15,7 +15,6 @@ require (
 	go.opentelemetry.io/otel/metric v1.26.0
 	go.opentelemetry.io/otel/trace v1.26.0
 	go.uber.org/goleak v1.3.0
-	go.uber.org/multierr v1.11.0
 	go.uber.org/zap v1.27.0
 )
 
@@ -44,6 +43,7 @@ require (
 	go.opentelemetry.io/otel/exporters/prometheus v0.48.0 // indirect
 	go.opentelemetry.io/otel/sdk v1.26.0 // indirect
 	go.opentelemetry.io/otel/sdk/metric v1.26.0 // indirect
+	go.uber.org/multierr v1.11.0 // indirect
 	golang.org/x/net v0.24.0 // indirect
 	golang.org/x/sys v0.19.0 // indirect
 	golang.org/x/text v0.14.0 // indirect

processor/processorhelper/metadata.yaml

@@ -0,0 +1,81 @@
+type: processorhelper
+
+status:
+  class: pkg
+  stability:
+    beta: [traces, metrics, logs]
+  distributions: [core, contrib]
+
+telemetry:
+  metrics:
+    processor_accepted_spans:
+      enabled: true
+      description: Number of spans successfully pushed into the next component in the pipeline.
+      unit: 1
+      sum:
+        value_type: int
+        monotonic: true
+
+    processor_refused_spans:
+      enabled: true
+      description: Number of spans that were rejected by the next component in the pipeline.
+      unit: 1
+      sum:
+        value_type: int
+        monotonic: true
+
+    processor_dropped_spans:
+      enabled: true
+      description: Number of spans that were dropped.
+      unit: 1
+      sum:
+        value_type: int
+        monotonic: true
+
+    processor_accepted_metric_points:
+      enabled: true
+      description: Number of metric points successfully pushed into the next component in the pipeline.
+      unit: 1
+      sum:
+        value_type: int
+        monotonic: true
+
+    processor_refused_metric_points:
+      enabled: true
+      description: Number of metric points that were rejected by the next component in the pipeline.
+      unit: 1
+      sum:
+        value_type: int
+        monotonic: true
+
+    processor_dropped_metric_points:
+      enabled: true
+      description: Number of metric points that were dropped.
+      unit: 1
+      sum:
+        value_type: int
+        monotonic: true
+
+    processor_accepted_log_records:
+      enabled: true
+      description: Number of log records successfully pushed into the next component in the pipeline.
+      unit: 1
+      sum:
+        value_type: int
+        monotonic: true
+
+    processor_refused_log_records:
+      enabled: true
+      description: Number of log records that were rejected by the next component in the pipeline.
+      unit: 1
+      sum:
+        value_type: int
+        monotonic: true
+
+    processor_dropped_log_records:
+      enabled: true
+      description: Number of log records that were dropped.
+      unit: 1
+      sum:
+        value_type: int
+        monotonic: true