Update docs for default tenant/namespace

Author: onobc

spring-pulsar-docs/src/main/antora/modules/ROOT/nav.adoc

@@ -21,6 +21,7 @@
 *** xref:reference/reactive-pulsar/reactive-message-consumption.adoc[]
 *** xref:reference/tombstones-reactive.adoc[]
 ** xref:reference/topic-resolution.adoc[]
+** xref:reference/default-tenant-namespace.adoc[]
 ** xref:reference/custom-object-mapper.adoc[]
 ** xref:reference/pulsar-admin.adoc[]
 ** xref:reference/pulsar-function.adoc[]

spring-pulsar-docs/src/main/antora/modules/ROOT/pages/reference/pulsar-admin.adoc

@@ -45,3 +45,11 @@ PulsarTopic partitionedTopic(PulsarTopicBuilder topicBuilder) {
         .build();
 }
 ----
+
+[[pulsar-topic-builder]]
+[NOTE]
+====
+When using Spring Boot the `PulsarTopicBuilder` is a registered bean that is configured with default values for domain, tenant, and namespace.
+You can simply inject the builder where needed.
+Otherwise, use one of the `PulsarTopicBuilder` constructors directly.
+====