Pull channels and handlers metrics outside of IntegrationMBeanExporter

After extraction IntegrationManagement abstraction we don't need to have JMX enabled to collection metrics. Therefore we don't need to add spring-integration-jmx dependency just for case to gather channel metrics.

Create component like org.springframework.integration.support.management.MetricsReader and pull getChannelMetrics(), getSourceMetrics() etc. methods from the IntegrationMBeanExporter.

Spring Boot's SpringIntegrationMetricReader has to be refactored respectively together with the drop of required now spring-integration-jmx dependency.