[Meta ] Use LS_JAVA_HOME in favor of JAVA_HOME

[andsel]

Logstash launch shell scripts uses the JAVA_HOME to identify a JDK configured by the user, that environment variable could be too generic and Logstash should have a dedicated LS_JAVA_HOME.
This issue tracks the task to do in order to manage this transition.

• modify launch scripts (bash and cmd) to use LS_JAVA_HOME giving precedence on this over the standard JAVA_HOME Introduce LS_JAVA_HOME environment variable #13204
• deprecate the JAVA_HOME on 7.x (but allow it to be used) Deprecate JAVA_HOME preferring LS_JAVA_HOME #13207
• backport the above PRs to 7.x (Deprecate JAVA_HOME preferring LS_JAVA_HOME #13207 and Introduce LS_JAVA_HOME environment variable #13204) [backport 7.x] Use LS_JAVA_HOME in favor of JAVA_HOME #12725 #13213
• remove completely the JAVA_HOME variable from scripts for version 8.0 Removed JAVA_HOME using only LS_JAVA_HOME #13214

[andsel]

Elasticsearch done a similar transition in elastic/elasticsearch#69149

[andsel]

Close because all the PRs landed.