Standardize error message thrown when a feature is not available

[jmooring]

I'd like to standardize the error message thrown when a particular feature is not available in the current version edition. This change would make this section of the documentation a bit simpler:

https://gohugo.io/troubleshooting/faq/#an-error-message-indicates-that-a-feature-is-not-available-why

I will handle this if this proposal is accepted.