Polishing.

Adjust visibility of CassandraObservationSupplier.

See #1321
Original pull request: #1322

Author: gregturn

spring-data-cassandra/src/main/java/org/springframework/data/cassandra/observability/CassandraObservationSupplier.java

@@ -22,9 +22,10 @@
  *
  * @author Mark Paluch
  * @author Marcin Grzejszczak
+ * @author Greg Turnquist
  * @since 4.0
  */
-interface CassandraObservationSupplier {
+public interface CassandraObservationSupplier {
 
 	/**
 	 * @return the observation

src/main/asciidoc/reference/observability.adoc

@@ -16,20 +16,20 @@ class ObservabilityConfiguration {
   @Bean
   public ObservableCqlSessionFactoryBean observableCqlSession(CqlSessionBuilder builder,
                                                               ObservationRegistry registry) {
-    return new ObservableCqlSessionFactoryBean(builder, registry);                        <1>
+    return new ObservableCqlSessionFactoryBean(builder, registry); // <1>
   }
 
   @Bean
   public ObservableReactiveSessionFactoryBean observableReactiveSession(CqlSession session,
                                                               ObservationRegistry registry) {
-    return new ObservableReactiveSessionFactoryBean(session, registry);                   <2>
+    return new ObservableReactiveSessionFactoryBean(session, registry); // <2>
   }
 }
 ----
 
 <1> Wraps the CQL session object to observe Cassandra statement execution.
 Also, registers `ObservationRequestTracker.INSTANCE` with the `CqlSessionBuilder`.
-<1> Wraps a CQL session object to observe reactive Cassandra statement execution.
+<2> Wraps a CQL session object to observe reactive Cassandra statement execution.
 ====
 
 include::../../../../target/_conventions.adoc[]