Audit Puppet Server strings for externalization issues

Review the formatting of existing user-facing strings in Puppet Server and fix formatting issues that are problematic for translators.
For some context, see PE-14216 and the Confluence page.
Contribute to the Confluence page if you identify additional issues.

This will largely look like translating string concatenation using (str "foo" x "bar") to (format "foo %s bar" x).

A thing to look out for in this ticket is trying to leave the strings that will be externalized in a format that is easily machine findable/replaceable. This might not be possible, so this is partially an R&D task.