Evaluate .Hugo.Environment variable for defining production build

[tlindsay42]

Closes #453

[tlindsay42]

Everything looks good with implementing these changes on my end via overrides, but still new to all this and wasn't sure of what exactly this with call did: /layouts/_default/baseof.html#42, nor the proper way to update it if necessary to evaluate the other options for specifying a production environment build. If this statement doesn't need to be updated, then this is ready for review.

?

[regisphilibert]

Hey and thank you, this PR does make sense but this is a dangerous breaking change as this would make every project without a HUGO_ENV variable set to be considered production. Everybody would have to update their non-production deployed branches, PRs, staging to explicitly set a HUGO_ENV=development

This is a default of Hugo that I never quite aligned with. Making every project's environment default to production is problematic.

I've thought about creating an IsProduction returning partial that would preserve the former behaviour while introducing hugo.Environment but cannot think of one. Can you?

[tlindsay42]

I can't either, and not accepting this makes sense in retrospect due to the risks. Oh well.