[chore][extension/bearertokenauth] Enable goleak check (open-telemetry#31154)

**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 adds `goleak` checks on the `bearertokenauthextension` extension to
help ensure no goroutines are being leaked. This is a test only change.

**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.

Author: crobert-1

extension/bearertokenauthextension/bearertokenauth_test.go

@@ -160,6 +160,7 @@ func TestBearerTokenFileContentUpdate(t *testing.T) {
 
 	assert.Nil(t, bauth.Start(context.Background(), componenttest.NewNopHost()))
 	assert.Error(t, bauth.Start(context.Background(), componenttest.NewNopHost()))
+	defer func() { assert.NoError(t, bauth.Shutdown(context.Background())) }()
 
 	token, err := os.ReadFile(bauth.filename)
 	assert.NoError(t, err)

extension/bearertokenauthextension/go.mod

@@ -12,6 +12,7 @@ require (
 	go.opentelemetry.io/collector/extension/auth v0.94.1
 	go.opentelemetry.io/otel/metric v1.23.0
 	go.opentelemetry.io/otel/trace v1.23.0
+	go.uber.org/goleak v1.3.0
 	go.uber.org/zap v1.26.0
 	google.golang.org/grpc v1.61.0
 )

extension/bearertokenauthextension/package_test.go

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