ensure minor/patch versions ship with same major version of plugins

Shipping different majors versions of a plugin within a minor/patch version of logstash can cause surprises to users not just with new behaviours and configurations no longer starting, but also there's higher chance of a bug sneaking in since major versions usually come from big changes.

We've been bit by this several times and, even though we try to enforce this constraint manually by curating the .lock file in the right branch, this must be embedded into our build/release process so there's less room for mistakes.