Modify the logical for getting schema compatibility strategy (#5785)

### Motivation
Modify the logical for getting schema compatibility strategy, if schemaCompatibilityStrategy = SchemaCompatibilityStrategy.UNDEFINED return the SchemaAutoUpdateCompatibilityStrategy. 

### Verifying this change
Add the tests for it

pulsar-broker/src/main/java/org/apache/pulsar/broker/admin/impl/NamespacesBase.java

@@ -2044,7 +2044,13 @@ public abstract class NamespacesBase extends AdminResource {
 
     protected SchemaCompatibilityStrategy internalGetSchemaCompatibilityStrategy() {
         validateAdminAccessForTenant(namespaceName.getTenant());
-        return getNamespacePolicies(namespaceName).schema_compatibility_strategy;
+        Policies policies = getNamespacePolicies(namespaceName);
+        SchemaCompatibilityStrategy schemaCompatibilityStrategy = policies.schema_compatibility_strategy;
+        if (schemaCompatibilityStrategy == SchemaCompatibilityStrategy.UNDEFINED){
+            schemaCompatibilityStrategy = SchemaCompatibilityStrategy
+                    .fromAutoUpdatePolicy(policies.schema_auto_update_compatibility_strategy);
+        }
+        return schemaCompatibilityStrategy;
     }
 
     @Deprecated

pulsar-broker/src/test/java/org/apache/pulsar/schema/compatibility/SchemaCompatibilityCheckTest.java

@@ -45,6 +45,7 @@ import java.util.concurrent.ThreadLocalRandom;
 
 import static org.apache.pulsar.common.naming.TopicName.PUBLIC_TENANT;
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
 
 
 @Slf4j
@@ -233,6 +234,9 @@ public class SchemaCompatibilityCheckTest extends MockedPulsarServiceBaseTest {
                 Sets.newHashSet(CLUSTER_NAME)
         );
 
+        assertEquals(admin.namespaces().getSchemaCompatibilityStrategy(namespaceName.toString()),
+                SchemaCompatibilityStrategy.FULL);
+        
         admin.namespaces().setSchemaCompatibilityStrategy(namespaceName.toString(), schemaCompatibilityStrategy);
         admin.schemas().createSchema(fqtn, Schema.AVRO(Schemas.PersonOne.class).getSchemaInfo());
 

pulsar-client-tools/src/main/java/org/apache/pulsar/admin/cli/CmdNamespaces.java

@@ -1082,7 +1082,7 @@ public class CmdNamespaces extends CmdBase {
         }
     }
 
-    @Parameters(commandDescription = "Get the schema auto-update strategy for a namespace")
+    @Parameters(commandDescription = "Get the schema auto-update strategy for a namespace", hidden = true)
     private class GetSchemaAutoUpdateStrategy extends CliCommand {
         @Parameter(description = "tenant/namespace", required = true)
         private java.util.List<String> params;
@@ -1095,7 +1095,7 @@ public class CmdNamespaces extends CmdBase {
         }
     }
 
-    @Parameters(commandDescription = "Set the schema auto-update strategy for a namespace")
+    @Parameters(commandDescription = "Set the schema auto-update strategy for a namespace", hidden = true)
     private class SetSchemaAutoUpdateStrategy extends CliCommand {
         @Parameter(description = "tenant/namespace", required = true)
         private java.util.List<String> params;