Avoid addShutdownHook to JVM during its shutdown (#5524)

Motivation:

Currently a JVM shutdown hook is added when DefaultClientFactory is used
for the first time
([code](https://github.com/line/armeria/blob/main/core/src/main/java/com/linecorp/armeria/client/DefaultClientFactory.java#L80-L83)).
It is possible that a JVM shutdown hook is being added after the JVM has
started its shutdown and results in an exception below:
```
Caused by: java.lang.IllegalStateException: Shutdown in progress
    at java.base/java.lang.ApplicationShutdownHooks.add(ApplicationShutdownHooks.java:66)
    at java.base/java.lang.Runtime.addShutdownHook(Runtime.java:216)
    at grpc_shaded.com.linecorp.armeria.client.DefaultClientFactory.<clinit>(DefaultClientFactory.java:79)
    ... 24 more
```

Modifications:
- Skip adding the hook if we explicitly disabled it.
- Add try-catch for ` java.lang.IllegalStateException`

Result:
- Closes #5494

---------

Co-authored-by: jrhee17 <[email protected]>

Author: thachlp

Diff for: core/src/main/java/com/linecorp/armeria/client/DefaultClientFactory.java

@@ -77,11 +77,15 @@ final class DefaultClientFactory implements ClientFactory {
 
     static {
         if (DefaultClientFactory.class.getClassLoader() == ClassLoader.getSystemClassLoader()) {
-            Runtime.getRuntime().addShutdownHook(new Thread(() -> {
-                if (!shutdownHookDisabled) {
-                    ClientFactory.closeDefault();
-                }
-            }));
+            try {
+                Runtime.getRuntime().addShutdownHook(new Thread(() -> {
+                    if (!shutdownHookDisabled) {
+                        ClientFactory.closeDefault();
+                    }
+                }));
+            } catch (IllegalStateException e) {
+                logger.debug("Skipped adding a shutdown hook to the DefaultClientFactory.", e);
+            }
         }
     }