localizability (L12y) improvements to string resources

This ticket contains proposed improvements to some string resources that use label.a_an*(), improving their L12Y (localizability).

Affected file:

• https://github.com/puppetlabs/puppet/blob/master/lib/puppet/pops/issues.rb

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The label_provider is located here: 

https://github.com/puppetlabs/puppet/blob/master/lib/puppet/pops/label_provider.rb

This file should also be referred to when making decisions just in case:

https://github.com/puppetlabs/puppet/blob/master/lib/puppet/pops/model/model_label_provider.rb