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.
This change both speeds up specs (less strings to allocate) and helps catch
cases where methods in Discourse are mutating inputs.
Overall we will be migrating everything to use #frozen_string_literal: true
it will take a while, but this is the first and safest move in this direction
* Remove use of 0 in favor of `TrustLevel.levels[:newuser]`.
* Consolidate two tests into a single one.
* Test that disabling the feature works.
* Avoid loading full ActiveRecord object in test when we only need to
know the existence of the record.
