* Add gauges for queue channel size
The `QueueChannel` provides a current size and remaining capacity metrics
* Add Micrometer gauges into `QueueChannel` to expose the current values
of the size and remaining capacity
**Cherry-pick to 5.3.x, 5.2.x & 5.1.x**
* * Revert `@SuppressWarnings("unchecked")` for test
* Document new gauges for queue channel
* * Fix IntegrationManagementConfigurer for NPE on `metricsCaptor`
* Fix wording in meter descriptions
Co-authored-by: Michel Jung <michel.jung89@gmail.com>
Co-authored-by: Michel Jung <michel.jung89@gmail.com>
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