[chore][service/internal/proctelemetry] Enable goleak check (#9227)

**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.-->
Add `goleak` to detect leaks in tests. Leaking goroutines were detected
that were caused by a dependency that we can ignore
(`go.opencensus.io/stats/view.(*worker).start`), some `Shutdown` calls
were also added that were missing.

**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.

service/internal/proctelemetry/config_test.go

@@ -339,7 +339,15 @@ func TestMetricReader(t *testing.T) {
 	}
 	for _, tt := range testCases {
 		t.Run(tt.name, func(t *testing.T) {
-			_, _, err := InitMetricReader(context.Background(), tt.reader, make(chan error))
+			reader, server, err := InitMetricReader(context.Background(), tt.reader, make(chan error))
+			defer func() {
+				if reader != nil {
+					assert.NoError(t, reader.Shutdown(context.Background()))
+				}
+				if server != nil {
+					assert.NoError(t, server.Shutdown(context.Background()))
+				}
+			}()
 			assert.Equal(t, tt.err, err)
 		})
 	}
@@ -691,7 +699,12 @@ func TestSpanProcessor(t *testing.T) {
 	}
 	for _, tt := range testCases {
 		t.Run(tt.name, func(t *testing.T) {
-			_, err := InitSpanProcessor(context.Background(), tt.processor)
+			processor, err := InitSpanProcessor(context.Background(), tt.processor)
+			defer func() {
+				if processor != nil {
+					assert.NoError(t, processor.Shutdown(context.Background()))
+				}
+			}()
 			assert.Equal(t, tt.err, err)
 		})
 	}

service/internal/proctelemetry/package_test.go

@@ -0,0 +1,17 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package proctelemetry
+
+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"))
+}