[chore][internal/e2e] Enable goleak check (#9223)

**Description:** <Describe what has changed.>
<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
Leaking goroutines were detected that were caused by a dependency that
we can ignore (`go.opencensus.io/stats/view.(*worker).start`), as well
as a missing server close call.

**Link to tracking Issue:** <Issue number if applicable>
#9165 

**Testing:** <Describe what testing was performed and which tests were
added.>
Added check is passing as well as existing tests.

internal/e2e/go.mod

@@ -17,6 +17,7 @@ require (
 	go.opentelemetry.io/collector/pdata v1.0.0
 	go.opentelemetry.io/collector/receiver v0.91.0
 	go.opentelemetry.io/collector/receiver/otlpreceiver v0.91.0
+	go.uber.org/goleak v1.3.0
 )
 
 require (

internal/e2e/otlphttp_test.go

@@ -250,6 +250,7 @@ func TestIssue_4221(t *testing.T) {
 		spanID := span.SpanID()
 		assert.Equal(t, "e5513c32795c41b9", hex.EncodeToString(spanID[:]))
 	}))
+	defer func() { svr.Close() }()
 
 	exp := startTracesExporter(t, "", svr.URL)
 

internal/e2e/package_test.go

@@ -0,0 +1,17 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package e2e
+
+import (
+	"testing"
+
+	"go.uber.org/goleak"
+)
+
+// The IgnoreTopFunction call prevents catching the leak generated by opencensus
+// defaultWorker.Start which at this time is part of the package's init call.
+// See https://github.com/open-telemetry/opentelemetry-collector/issues/9165#issuecomment-1874836336 for more context.
+func TestMain(m *testing.M) {
+	goleak.VerifyTestMain(m, goleak.IgnoreTopFunction("go.opencensus.io/stats/view.(*worker).start"))
+}