It's very easy to forget to add `require 'rails_helper'` at the top of every core/plugin spec file, and omissions can cause some very confusing/sporadic errors.
By setting this flag in `.rspec`, we can remove the need for `require 'rails_helper'` entirely.
- Define the CSP based on the requested domain / scheme (respecting force_https)
- Update EnforceHostname middleware to allow secondary domains, add specs
- Add URL scheme to anon cache key so that CSP headers are cached correctly
* FEATURE: allow plugins and themes to extend the default CSP
For plugins:
```
extend_content_security_policy(
script_src: ['https://domain.com/script.js', 'https://your-cdn.com/'],
style_src: ['https://domain.com/style.css']
)
```
For themes and components:
```
extend_content_security_policy:
type: list
default: "script_src:https://domain.com/|style_src:https://domain.com"
```
* clear CSP base url before each test
we have a test that stubs `Rails.env.development?` to true
* Only allow extending directives that core includes, for now
