Include the puppetserver_gem package provider with core Puppet

The core puppet types and providers include a puppet_gem provider for the package resource that knows how to interact with the Ruby interpreter bundled with the puppet-agent package.

The puppetserver service also bundles its own JRuby interpreter and requires the used of the puppetserver gem command to install packages. There is an unsupported module, puppetlabs/puppetserver_gem, that adds a puppetserver_gem provider for package resources that fills an analogous role.

However, having this provider de-coupled from the Puppet core means it can be broken by changes in the core in a way that interferes with upgrades. PUP-6488 was one such instance where the parent Gem provider was altered in a way that was incompatible with puppet_gem and puppetserver_gem. Both providers were patched, but the breakage in puppet_gem was automatically resolved by an upgrade while the breakage in puppetserver_gem requires users to discover, understand, and then upgrade the module.

To prevent these sorts of issues, puppetserver_gem provider should be bundled along with puppet_gem by puppet-agent.