Make gradle the main entrypoint for any logstash related build task

[donoghuc]

Logstash uses gradle, rake and make as build tools. Gradle is used to manage a java/ruby environment. Standardizing on using gradle as an entrypoint for any top level build toolchain allows us to express dependencies in the gradle planner. In addition to making gradle the entrypoint, we remove the need to call gradle from the other build tools. There exists a pattern today whereby rake shells out to gradle. This is brittle and convolutes dependency resolution. Refactor any rake task that shells out to gradle to express that in gradle. Note that gradle can (and should for the first iteration) call in to rake. Similarly rake may invoke make for the first iteration. This focuses purely on

1. Make every toolchain start with gradle
2. No intermediate tool (rake or make) may shell out to gradle

[donoghuc]

#18471 is a WIP with the result of a spike working through this. I'll push that forward for this issue.

[donoghuc]

Reminder to circle back to https://github.com/elastic/logstash/pull/18340/files#r2488030095 with this