INT-3387: MessageGroupStore Improvements

JIRA: https://jira.spring.io/browse/INT-3387,
https://jira.spring.io/browse/INT-3806

* Introduce
```
MessageGroupStore

void addMessagesToGroup(Object groupId, Message<?>... messages);
```
And implement it in all stores.

* Use new `addMessagesToGroup` where it is reasonable, e.g. `DelayHandler`
* Optimize test-case to use a new store method (where it is possible)
* Fix timing delays in the `JdbcMessageStoreTests`
* Introduce `PersistentMessageGroup`
* Add `AbstractMessageGroupStore#proxyMessageGroupForLazyLoad` to wrap the raw `MessageGroup` to the `PersistentMessageGroup` for lazy-load
* Rework `MessageGroupMetadata` do not be `immutable` and allow to store/restore in the `AbstractKeyValueMessageStore` only the `MessageGroupMetadata`
* Refactor `ResequencingMessageHandler` and `SequenceSizeReleaseStrategy` a bit for better performance when interact with the `MessageGroup`
* Add `AbstractMessageGroupStore#setLazyLoadMessageGroups` to switch off the `lazy-load` behavior and restore the previous full `MessageGroup` logic
* Add `What's New` note and `message-store.adoc` paragraph for the lazy-load functionality

`GroupType.PERSISTENT` and not lazy by default

PR Comments

Fix `JdbcMessageStoreTests` timing issues

Address PR comments

* Add performance test to the `ConfigurableMongoDbMessageGroupStoreTests`
* Add JavaDocs for the `MessageGroupFactory` methods
* Add `log4j.properties` into the `test` MongoDB module for better traceability
* Fix `JdbcMessageStore#getOneMessageFromGroup()` over the `doPollForMessage()` delegation.
The `jdbcTemplate.queryForObject()` requires exactly one and only one raw in `resultSet`
* Add performance test results into the `message-store.adoc`

src/reference/asciidoc/message-store.adoc

@@ -94,3 +94,40 @@ This defaults to a `SimpleMessageGroupFactory` which produces `SimpleMessageGrou
 (`LinkedHashSet`) internal collection.
 Other possible options are `SYNCHRONISED_SET` and `BLOCKING_QUEUE`, where the last one can be used to reinstate the
 previous `SimpleMessageGroup` behavior.
+Also the `PERSISTENT` option is available. See the next section for more information.
+
+[[lazy-load-message-group]]
+==== Persistence MessageGroupStore and Lazy-Load
+
+Starting with _version 4.3_, all persistence `MessageGroupStore` s retrieve `MessageGroup` s and their `messages`
+from the store with the _Lazy-Load_ manner.
+In most cases it is useful for the Correlation `MessageHandler` s (<<aggregator>> and <<resequencer>>),
+when it would be an overhead to load entire `MessageGroup` from the store on each correlation operation.
+
+To switch off the lazy-load behavior the `AbstractMessageGroupStore.setLazyLoadMessageGroups(false)` option
+can be used from the configuration.
+
+Our performance tests for _lazy-load_ on MongoDB `MessageStore` (<<mongodb-message-store>>) and
+`<aggregator>` (<<aggregator>>)
+with custom `release-strategy` like:
+
+[source,xml]
+----
+<int:aggregator input-channel="inputChannel"
+                output-channel="outputChannel"
+                message-store="mongoStore"
+                release-strategy-expression="size() == 1000"/>
+
+----
+
+demonstrate this results for 1000 simple messages:
+
+....
+StopWatch 'Lazy-Load Performance': running time (millis) = 38918
+-----------------------------------------
+ms     %     Task name
+-----------------------------------------
+02652  007%  Lazy-Load
+36266  093%  Eager
+....
+

src/reference/asciidoc/whats-new.adoc

@@ -21,6 +21,11 @@ The `SimpleMessageGroupFactory` is provided for the `SimpleMessageGroup` with th
 factory for the standard `MessageGroupStore` implementations.
 See <<message-store>> for more information.
 
+==== PersistentMessageGroup
+
+The `PersistentMessageGroup`, - lazy-load proxy, - implementation is provided for persistent `MessageGroupStore` s,
+which return this instance for the `getMessageGroup()` when their `lazyLoadMessageGroups` is `true` (defaults).
+See <<message-store>> for more information.
 
 [[x4.3-general]]
 === General Changes