Enabling basic auth for local & prod environments doesn't work

Steps to reproduce:
1. Follow the docs to add local environment specific config for php basic auth
2. Load the site
3. Basic auth not requested / required

There should be a prompt to enter the username and password.

I think the way environment checks are incorporated into the plugin is very confusing. Environments should be opted in to explicitly by type or globally as required.

In the meantime though the plugin integration should be fixed so that the docs are accurate.

Acceptance criteria:

- [ ] ...