licensing: add new plans and enforce SSO
Created by: unknwon
This PR does two things:
- Adds new plans "business-0" and "enterprise-1".
- Requires a valid license for enabling any non-builtin authentication provider, i.e. taking SSO away from Free instances.
Warning logs are printed to the console and site alerts are shown to the site admin:
Test plan
Unit tests and manual e2e tests.
Part of https://github.com/sourcegraph/sourcegraph/issues/40064