change the build task in PSH to use PDK::Module::Build

The puppetlabs_spec_helper build rake task (https://github.com/puppetlabs/puppetlabs_spec_helper/blob/2c887fc0e68c3c8f5904997105c4f474a84e800c/lib/puppetlabs_spec_helper/rake_tasks.rb#L105-L114) used by puppet-blacksmith and others to build modules is using the deprecated (removed in puppet6; see PUP-8762, PUP-8763) module build subcommand.

To ensure that this continues to work going forward, change the rake task to use the PDK's PDK::Module::Build instead.

This also requires adding the pdk gem as a dependency to puppetlabs_spec_helper. To ensure that this does not break existing workflows, it requires PDK-1099 to be released as a gem first, and the dependency to be versioned appropriately.

When implementing this, make sure that the build task still is able to build non-pdk-ified modules in the end. This is very important as puppet-blacksmith is also used with non-converted modules.