Fix#903
Use 'application' as the trigger name consistently.
Since 'application' would be a too generic name for
the Exporter bean, use a BeanPostProcessor to install
the exporter in the `MetricExporters` bean.
Additional updates
- rename binding to `applicationMetrics` (we can decide later how
the channel is named)
- remove the default setting for `spring.metrics.export`
- Improve documentation
Fix#904
Docs updates
Properly escape asciidoc control characters
d6fe841a63