The `active` param on the create user endpoint requires that an api key
is used in the request header otherwise it is ignored, so adding this
distinction to the api docs.
Discourse users and associated accounts are created or updated when a
user logins or connects the account using their account preferences.
This new API can be used to create associated accounts and users too,
if necessary.
Due to the way that rswag expands shared components we were getting this
warning when linting our api docs:
```
Component: "user_response" is never used.
```
This change refactors the `api/users_spec.rb` file so that it uses the
new way of doing things with a separate `user_get_response.json` schema
file rather then the old way of loading a shared response inside of the
swagger_helper.rb file.
