Retain non-default filters and plugins after apt/.deb upgrade

Every time that I upgrade Logstash, which sometimes could even be automatic through unattended_upgrades, I need to install non-default filters and plugins that are being used in my configuration since they get wiped out. It's cumbersome and creates extra work for users.

It would be great if these were preserved upon update... I know it's a little complicated since each version has its own own jruby/ruby environment and all that, but I'm sure there should be some way to capture a list of installed non-default Logstash plugins, and leverage a post-inst hook within the .deb package or some other mechanism to ensure they will be present.