[chore][exporter/kafka] Enable goleak check (open-telemetry#30961)

**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.-->
This enables the `goleak` package to check the Kafka exporter for
goroutine leaks. This is a test only change, a few `Shutdown` calls were
missing from tests.

**Link to tracking Issue:** <Issue number if applicable>
open-telemetry#30438

**Testing:** <Describe what testing was performed and which tests were
added.>
All existing tests are passing as well as added `goleak` check.

---------

Co-authored-by: Pablo Baeyens <pbaeyens31+github@gmail.com>

exporter/kafkaexporter/factory_test.go

@@ -131,6 +131,7 @@ func TestCreateMetricExporter(t *testing.T) {
 			}
 			assert.NoError(t, err, "Must not error")
 			assert.NotNil(t, exporter, "Must return valid exporter when no error is returned")
+			assert.NoError(t, exporter.Shutdown(context.Background()))
 		})
 	}
 }
@@ -205,6 +206,7 @@ func TestCreateLogExporter(t *testing.T) {
 			}
 			assert.NoError(t, err, "Must not error")
 			assert.NotNil(t, exporter, "Must return valid exporter when no error is returned")
+			assert.NoError(t, exporter.Shutdown(context.Background()))
 		})
 	}
 }
@@ -279,6 +281,7 @@ func TestCreateTraceExporter(t *testing.T) {
 			}
 			assert.NoError(t, err, "Must not error")
 			assert.NotNil(t, exporter, "Must return valid exporter when no error is returned")
+			assert.NoError(t, exporter.Shutdown(context.Background()))
 		})
 	}
 }

exporter/kafkaexporter/go.mod

@@ -24,6 +24,7 @@ require (
 	go.opentelemetry.io/collector/semconv v0.95.0
 	go.opentelemetry.io/otel/metric v1.23.1
 	go.opentelemetry.io/otel/trace v1.23.1
+	go.uber.org/goleak v1.3.0
 	go.uber.org/multierr v1.11.0
 	go.uber.org/zap v1.27.0
 )

exporter/kafkaexporter/package_test.go

@@ -0,0 +1,14 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package kafkaexporter
+
+import (
+	"testing"
+
+	"go.uber.org/goleak"
+)
+
+func TestMain(m *testing.M) {
+	goleak.VerifyTestMain(m)
+}