[pulsar-client] Add conf backoff values (apache#12520)

* add conf backoff values

* Apply suggestions from code review

Co-authored-by: Callum Duffy <callum.duffy@toasttab.com>
Co-authored-by: Michael Marshall <mikemarsh17@gmail.com>

### Motivation

Allowing services waiting on pulsar container etc to use the backoff values given in the config when the client is initialised. Using a service where i handle the future on my side, but i feel this should be in the service as is!

### Modifications

Edit the values used for the backoff to use the client values.
Defaults are the exact same as the values used previous to this change.

pulsar-client/src/main/java/org/apache/pulsar/client/impl/PulsarClientImpl.java

@@ -947,9 +947,9 @@ public CompletableFuture<PartitionedTopicMetadata> getPartitionedTopicMetadata(S
             TopicName topicName = TopicName.get(topic);
             AtomicLong opTimeoutMs = new AtomicLong(conf.getLookupTimeoutMs());
             Backoff backoff = new BackoffBuilder()
-                    .setInitialTime(100, TimeUnit.MILLISECONDS)
+                    .setInitialTime(conf.getInitialBackoffIntervalNanos(), TimeUnit.NANOSECONDS)
                     .setMandatoryStop(opTimeoutMs.get() * 2, TimeUnit.MILLISECONDS)
-                    .setMax(1, TimeUnit.MINUTES)
+                    .setMax(conf.getMaxBackoffIntervalNanos(), TimeUnit.NANOSECONDS)
                     .create();
             getPartitionedTopicMetadata(topicName, backoff, opTimeoutMs,
                                         metadataFuture, new ArrayList<>());