Remove __v1_type tag

- Metrics that were received initially as v1 metrics include a __v1_type
  tag to indicate the type of v1 metric that was emitted.
- This causes issues for the prometheus exporter as:
  'Label names beginning with __ (two "_") are reserved for internal use.'
  https://prometheus.io/docs/concepts/data_model/
- Remove the __v1_type tag during the conversion so that these metrics
  will be acceptable to prometheus exporters.

Fixes:

  "__v1_type" is not a valid label name for metric

Signed-off-by: Rebecca Roberts <robertsre@vmware.com>

src/pkg/otelcolclient/otelcolclient.go

@@ -173,7 +173,7 @@ func attributes(e *loggregator_v2.Envelope) []*commonpb.KeyValue {
 	}
 
 	for k, v := range e.Tags {
-		if k == "instance_id" || k == "source_id" {
+		if k == "instance_id" || k == "source_id" || k == "__v1_type" {
 			continue
 		}
 

src/pkg/otelcolclient/otelcolclient_test.go

@@ -255,6 +255,20 @@ var _ = Describe("Client", func() {
 					Expect(cmp.Diff(actualAtts, expectedAtts, protocmp.Transform(), sortFunc)).To(BeEmpty())
 				})
 			})
+
+			Context("when the envelope has been converted from a v1 representation", func() {
+				BeforeEach(func() {
+					envelope.Tags["__v1_type"] = "ValueMetric"
+				})
+
+				It("drops the __v1_type tag", func() {
+					var msr *colmetricspb.ExportMetricsServiceRequest
+					Expect(spyMSC.requests).To(Receive(&msr))
+
+					actualAtts := msr.GetResourceMetrics()[0].GetScopeMetrics()[0].GetMetrics()[0].GetGauge().GetDataPoints()[0].GetAttributes()
+					Expect(actualAtts).ToNot(ContainElement(HaveField("Key", "__v1_type")))
+				})
+			})
 		})
 
 		Context("when given a counter", func() {