* add onPreResponse interceptor

* use onPreResponse interceptor to add license sign

* expose registerPreResponse to plugins

* refresh for license update get the most fresh license

* license plugin injects own header for signature:  'kbn-license-sig'

* add integration tests for license type and license header

* switch config to duration

* don't run interceptor on anon paths. add tests

* add functional tests for licensing plugin

* regen docs

* fix test in security due to updated mocks;

* update snapshots accoring to new mock implementation

* migrate license expired banner to NP

* add readme for the licensing plugin

* remove outdated import. licensing has separate functional tests

* add tag for test to run on CI

* regen docs

* Update x-pack/plugins/licensing/README.md

Co-Authored-By: Josh Dover <me@joshdover.com>

* update tests