(CAT-1984) - Add forge auth to fixtures module install

Prior to this commit, users were unable to perform the install of
modules which required forge authorization.

This change introduces the ability to know install modules behind
authorization, by referencing an env variable set by the user, and
appending this onto the `puppet module install` operation if present.

Author: jordanbreen28

README.md

@@ -211,6 +211,17 @@ When specifying the repo source of the fixture you have a few options as to whic
    puppet_version: '>= 6.0.0'
    ```
 
+Using Forge Authorization
+==============
+
+In order to perform forge operations which required authorization, such as installing premium modules, you can export your forge api key as an environment variable in your terminal.
+
+```bash
+FORGE_API_KEY='your_api_key'
+```
+
+puppetlabs_spec_helper will then automatically append this key to all `puppet module install` requests when running `rake spec_prep`.
+
  **Notes:**
 
  * `ref` and `branch` can be used together to get a specific revision on a specific branch

lib/puppetlabs_spec_helper/tasks/fixtures.rb

@@ -379,6 +379,9 @@ def download_module(remote, opts)
           flags = " #{opts['flags']}" if opts['flags']
         end
 
+        forge_token = ENV.fetch('FORGE_API_KEY', nil)
+        flags += " --forge_authorization \"Bearer #{forge_token}\"" if forge_token
+
         return false if File.directory?(target) && (ref.empty? || opts['ref'] == module_version(target))
 
         # The PMT cannot handle multi threaded runs due to cache directory collisons