[cmd/opampsupervisor] Fix memory leak and enable goleak (#30496)

**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.-->

`NewSupervisor` starts two goroutines, one for the health check ticker
and another running the agent process. Each was causing a leak. To
resolve the health check ticker goroutine leak a `Stop` call has been
added to it during shutdown. To resolve the agent process leak a wait
group has been added (to make sure shutdown blocks until the agent
process is completely shutdown), and a `break` statement has been
changed to `return`. The `break` statement was only breaking out of the
`select` statement, but since it's nested within a `for` loop, the loop
just kept going instead of completing successfully.


This also enables `goleak` checks for `cmd/opampsupervisor` and
`cmd/opampsupervisor/supervisor` packages

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

**Testing:** <Describe what testing was performed and which tests were
added.>
Existing tests and new `goleak` checks are passing.

.chloggen/goleak_opampsupervisor.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: bug_fix
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: cmd/opampsupervisor
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Fix memory leak on shutdown
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [30438]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: []

cmd/opampsupervisor/package_test.go

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

cmd/opampsupervisor/supervisor/supervisor.go

@@ -14,6 +14,7 @@ import (
 	"net/http"
 	"os"
 	"sort"
+	"sync"
 	"sync/atomic"
 	"text/template"
 	"time"
@@ -100,6 +101,7 @@ type Supervisor struct {
 	opampClient client.OpAMPClient
 
 	shuttingDown bool
+	supervisorWG sync.WaitGroup
 
 	agentHasStarted               bool
 	agentStartHealthCheckAttempts int
@@ -160,7 +162,12 @@ func NewSupervisor(logger *zap.Logger, configFile string) (*Supervisor, error) {
 	}
 
 	s.startHealthCheckTicker()
-	go s.runAgentProcess()
+
+	s.supervisorWG.Add(1)
+	go func() {
+		defer s.supervisorWG.Done()
+		s.runAgentProcess()
+	}()
 
 	return s, nil
 }
@@ -698,7 +705,7 @@ func (s *Supervisor) runAgentProcess() {
 
 		case <-s.commander.Done():
 			if s.shuttingDown {
-				break
+				return
 			}
 
 			s.logger.Debug("Agent process exited unexpectedly. Will restart in a bit...", zap.Int("pid", s.commander.Pid()), zap.Int("exit_code", s.commander.ExitCode()))
@@ -782,6 +789,12 @@ func (s *Supervisor) Shutdown() {
 			s.logger.Error("Could not stop the OpAMP client", zap.Error(err))
 		}
 	}
+
+	if s.healthCheckTicker != nil {
+		s.healthCheckTicker.Stop()
+	}
+
+	s.supervisorWG.Wait()
 }
 
 func (s *Supervisor) onMessage(ctx context.Context, msg *types.MessageData) {