Resolves https://github.com/spring-projects/spring-integration/issues/3490 - also fix double import of `jmx.adoc` - also fix `redis.adoc` * Remove redundant repo in `docs.gradle` * Use `stylesheet.css` for `asciidoctorj` plugin config * Fix `stylesheet.css` to import `spring.css` from the same dir since they both are copied over there into the same dir * Fix link for JMX chapter from the `metrics.adoc` * Fix some inconsistency in the `amqp.adoc`