Create promotion job for the puppetserver-ca-cli gem

Currently whenever we release a new version of the CA CLI gem, we have to manually update simple files in both puppetserver and pe-pse for any branches that need the update (5.3.x and beyond). This can involve up to 6 PRs currently. We should have a jenkins job that automatically updates both projects for a given stream. For the time being, this should probably be relatively unmagical: the job should accept a gem version, a FOSS branch, and a PE branch, and update https://github.com/puppetlabs/puppetserver/blob/master/resources/ext/build-scripts/mri-gem-list.txt and https://github.com/puppetlabs/pe-puppet-server-extensions/blob/johnson/resources/ext/build-scripts/mri-gem-list.txt with the new version. If we ultimately want to chain these units together to update multiple streams on a gem release (right now we are shipping the same version to all branches), we can do that, but the job shouldn't do it automatically.

Open Question: should this work for an arbitrary gem?