Create a `Logging against ELK-stack` guide

[vy]

As agreed in the site structure document, create a "Logging against ELK-stack" guide such that

• Mention about JTL and ecs-logging-java
• Research on appenders – One can either use a SocketAppender targeted to Logstash (we have an example for this in log4j-layout-template-json-test/pom.xml) or write to files scraped by Beats. We need to evaluate the current status quo and share the most recent best practices.
• Ask for review from Elastic (We can ask using their Forums, it worked for @vy in the past.)
• If possible, retire/remove cloud.adoc
• Target 2.x, port to main