Polish contribution

The properties exposed by the ActiveMQ pooled connection factory are
quite specific and I felt it was arbitrary to expose some and not others.

However, the number of connections and the timeouts seem the most useful
so they have been kept and a `configuration` nested namespace can be
used to configure any additional settings.

The core properties have been renamed to be less "raw" and more compliant
with the structure of other properties. The documentation on fields has
also been aligned.

Closes gh-5372

spring-boot-docs/src/main/asciidoc/appendix-application-properties.adoc

@@ -727,12 +727,11 @@ content into your application; rather pick only the properties that you need.
 	spring.activemq.in-memory=true # Specify if the default broker URL should be in memory. Ignored if an explicit broker has been specified.
 	spring.activemq.password= # Login password of the broker.
 	spring.activemq.user= # Login user of the broker.
-	spring.activemq.pool.enabled=false # Specify if a PooledConnectionFactory should be created instead of a regular ConnectionFactory.
-    spring.activemq.pool.max-connections=1 # The maximum number of pooled Connections
-    spring.activemq.pool.max-sessions-per-connection=500 # The maximum number of active sessions per connection
-    spring.activemq.pool.time-between-eviction-runs-millis=-1 # The number of milliseconds to sleep between runs of the idle Connection eviction thread.
-    spring.activemq.pool.idle-time-millis=30000 # The idle timeout value for Connection's that are created by this pool (in Milliseconds)
-    spring.activemq.pool.expiry-time-millis=0 # Allow connections to expire, irrespective of load or idle time
+	spring.activemq.pool.configuration.*= # See PooledConnectionFactory
+	spring.activemq.pool.enabled=false # Whether a PooledConnectionFactory should be created instead of a regular ConnectionFactory.
+    spring.activemq.pool.expiry-timeout=0 # Connection expiration timeout in milliseconds.
+    spring.activemq.pool.idle-timeout=30000 # Connection idle timeout in milliseconds.
+    spring.activemq.pool.max-connections=1 # Maximum number of pooled connections.
 
 	# ARTEMIS ({sc-spring-boot-autoconfigure}/jms/artemis/ArtemisProperties.{sc-ext}[ArtemisProperties])
 	spring.artemis.embedded.cluster-password= # Cluster password. Randomly generated on startup by default.