BrokerService.unloadNamespaceBundlesGracefully() hangs and doesn't complete

**Describe the bug**

This behavior is currently seen in tests, but it might be a production code issue.

The call to `BrokerService.unloadNamespaceBundlesGracefully()` can hang and it doesn't complete.

Example stack trace:
```
"main" #1 prio=5 os_prio=0 cpu=10593.61ms elapsed=3533.21s tid=0x00007f7f60024370 nid=0xa9b waiting on condition [0x00007f7f650c5000]
java.lang.Thread.State: WAITING (parking)
at jdk.internal.misc.Unsafe.park(java.base@17.0.3/Native Method)
- parking to wait for <0x00000000cd700010> (a java.util.concurrent.CompletableFuture$Signaller)
at java.util.concurrent.locks.LockSupport.park(java.base@17.0.3/LockSupport.java:211)
at java.util.concurrent.CompletableFuture$Signaller.block(java.base@17.0.3/CompletableFuture.java:1864)
at java.util.concurrent.ForkJoinPool.unmanagedBlock(java.base@17.0.3/ForkJoinPool.java:3463)
at java.util.concurrent.ForkJoinPool.managedBlock(java.base@17.0.3/ForkJoinPool.java:3434)
at java.util.concurrent.CompletableFuture.waitingGet(java.base@17.0.3/CompletableFuture.java:1898)
at java.util.concurrent.CompletableFuture.get(java.base@17.0.3/CompletableFuture.java:2072)
at org.apache.pulsar.broker.service.BrokerService.lambda$unloadNamespaceBundlesGracefully$21(BrokerService.java:919)
at org.apache.pulsar.broker.service.BrokerService$$Lambda$738/0x00000008013ad960.accept(Unknown Source)
at java.lang.Iterable.forEach(java.base@17.0.3/Iterable.java:75)
at org.apache.pulsar.broker.service.BrokerService.unloadNamespaceBundlesGracefully(BrokerService.java:911)
at org.apache.pulsar.broker.service.BrokerService.unloadNamespaceBundlesGracefully(BrokerService.java:887)
at org.apache.pulsar.broker.service.BrokerService.closeAsync(BrokerService.java:732)
at org.apache.pulsar.broker.PulsarService.closeAsync(PulsarService.java:450)
at org.apache.pulsar.broker.PulsarService.close(PulsarService.java:372)
at org.apache.pulsar.functions.worker.PulsarFunctionTlsTest.tearDown(PulsarFunctionTlsTest.java:182)
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(java.base@17.0.3/Native Method)
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke(java.base@17.0.3/NativeMethodAccessorImpl.java:77)
at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(java.base@17.0.3/DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(java.base@17.0.3/Method.java:568)
at org.testng.internal.MethodInvocationHelper.invokeMethod(MethodInvocationHelper.java:132)
at org.testng.internal.MethodInvocationHelper.invokeMethodConsideringTimeout(MethodInvocationHelper.java:61)
at org.testng.internal.ConfigInvoker.invokeConfigurationMethod(ConfigInvoker.java:366)
at org.testng.internal.ConfigInvoker.invokeConfigurations(ConfigInvoker.java:320)
at org.testng.internal.TestInvoker.runConfigMethods(TestInvoker.java:701)
at org.testng.internal.TestInvoker.runAfterGroupsConfigurations(TestInvoker.java:677)
at org.testng.internal.TestInvoker.invokeMethod(TestInvoker.java:661)
at org.testng.internal.TestInvoker.invokeTestMethod(TestInvoker.java:174)
at org.testng.internal.MethodRunner.runInSequence(MethodRunner.java:46)
at org.testng.internal.TestInvoker$MethodInvocationAgent.invoke(TestInvoker.java:822)
at org.testng.internal.TestInvoker.invokeTestMethods(TestInvoker.java:147)
at org.testng.internal.TestMethodWorker.invokeTestMethods(TestMethodWorker.java:146)
at org.testng.internal.TestMethodWorker.run(TestMethodWorker.java:128)
at org.testng.TestRunner$$Lambda$191/0x0000000800dcb740.accept(Unknown Source)
at java.util.ArrayList.forEach(java.base@17.0.3/ArrayList.java:1511)
at org.testng.TestRunner.privateRun(TestRunner.java:764)
at org.testng.TestRunner.run(TestRunner.java:585)
at org.testng.SuiteRunner.runTest(SuiteRunner.java:384)
at org.testng.SuiteRunner.runSequentially(SuiteRunner.java:378)
at org.testng.SuiteRunner.privateRun(SuiteRunner.java:337)
at org.testng.SuiteRunner.run(SuiteRunner.java:286)
at org.testng.SuiteRunnerWorker.runSuite(SuiteRunnerWorker.java:53)
at org.testng.SuiteRunnerWorker.run(SuiteRunnerWorker.java:96)
at org.testng.TestNG.runSuitesSequentially(TestNG.java:1218)
at org.testng.TestNG.runSuitesLocally(TestNG.java:1140)
at org.testng.TestNG.runSuites(TestNG.java:1069)
at org.testng.TestNG.run(TestNG.java:1037)
at org.apache.maven.surefire.testng.TestNGExecutor.run(TestNGExecutor.java:135)
at org.apache.maven.surefire.testng.TestNGDirectoryTestSuite.executeSingleClass(TestNGDirectoryTestSuite.java:112)
at org.apache.maven.surefire.testng.TestNGDirectoryTestSuite.executeLazy(TestNGDirectoryTestSuite.java:123)
at org.apache.maven.surefire.testng.TestNGDirectoryTestSuite.execute(TestNGDirectoryTestSuite.java:90)
at org.apache.maven.surefire.testng.TestNGProvider.invoke(TestNGProvider.java:146)
at org.apache.maven.surefire.booter.ForkedBooter.invokeProviderInSameClassLoader(ForkedBooter.java:384)
at org.apache.maven.surefire.booter.ForkedBooter.runSuitesInProcess(ForkedBooter.java:345)
at org.apache.maven.surefire.booter.ForkedBooter.execute(ForkedBooter.java:126)
at org.apache.maven.surefire.booter.ForkedBooter.main(ForkedBooter.java:418)
```
[full thread dump](https://jstack.review?https://gist.github.com/lhotari/968ee78b2b6f708590fadc130d6a9d05)

**Expected behavior**

The root cause of the issue should be fixed instead of stopping to wait for the unloading to complete.

Start in BrokerService.java at unloadNamespaceBundlesGracefully, especially the CompletableFuture wait at lines 887-919 shown in the stack trace. Trace the closeAsync path from PulsarFunctionTlsTest.tearDown and consult the linked thread dump. Done means graceful unloading completes without hanging and the underlying cause is covered by a test.

Written by the indexing model from the issue text.