[Broker] Handle all exceptions from topic.addProducer (apache#6881)

Fixes apache#6872
Fixes apache#6416

If a producer tries to create a producer to a topic that is currently
unloading, we can get a `RuntimeException` from
`BrokerService.checkTopicNsOwnership` which is bubbled up through
`topic.addProducer`. By only handling a `BrokerServiceException` this
results in a future that never completes and results in producers not
being able to be created if this topic is scheduled back to this broker.

pulsar-broker/src/main/java/org/apache/pulsar/broker/service/ServerCnx.java

@@ -1007,7 +1007,7 @@ protected void handleProducer(final CommandProducer cmdProducer) {
                                 ServerError error = null;
                                 if(!existingProducerFuture.isDone()) {
                                     error = ServerError.ServiceNotReady;
-                                }else {
+                                } else {
                                     error = getErrorCode(existingProducerFuture);
                                     // remove producer with producerId as it's already completed with exception
                                     producers.remove(producerId);
@@ -1091,7 +1091,7 @@ protected void handleProducer(final CommandProducer cmdProducer) {
                                         producerFuture.completeExceptionally(
                                             new IllegalStateException("Producer created after connection was closed"));
                                     }
-                                } catch (BrokerServiceException ise) {
+                                } catch (Exception ise) {
                                     log.error("[{}] Failed to add producer to topic {}: {}", remoteAddress, topicName,
                                         ise.getMessage());
                                     ctx.writeAndFlush(Commands.newError(requestId,