Bringing back jar dependencies as managing tool for jars in LS

[purbon]

As is noted in elastic/logstash#3735 there is the interest to experiment on how to run jar-dependencies in a proper way within logstash, this plugin amoung others will be used as base work for it.

For now think about this PR as the playground to create a jar-dependencies based LS plugin.

[purbon]

Would you be so nice @ph to give me your thoughts on this? Thanks a lot for your time.

[talevy]

@purbon

I know this was probably forgotten about, but we can relook at the jar-dependencies thing.

if you take a look at https://github.com/logstash-plugins/logstash-filter-geoip now, you should see an example of how we should be using jar-dependencies for building our gems.

specifically, relying on rake tasks and setting jar-dependencies as a development dependency so it doesn't try to fetch more when people install the gem.

[jordansissel]

This plugin is deprecated for security reasons. More details, including a recommended alternative, available here: https://www.elastic.co/guide/en/logstash/current/plugins-inputs-log4j.html#_deprecation_notice