JIRA: https://jira.spring.io/browse/INT-3997
* Created the `H2ChannelMessageStoreQueryProvider` class for the
`ChannelMessageStoreQueryProvider` interface
* The `LongRunningIntegrationTest` class needs the
`RUN_LONG_INTEGRATION_TESTS` variable defined in the 'system'
and set in true. It to let work the test methods for the
`H2TxTimeoutMessageStoreTests` class
* Updated reference documentation about `ChannelMessageStoreQueryProvider`
* Polishing
c6821ec387