Create a shell script to create a new recipe stub

As track leads begin to work on Drupal CMS, they'll probably want to create new recipes. That takes a little bit of setup, so it's probably easier to script that boilerplate. This MR adds the following shell command:

ddev exec create_recipe drupal_cms_foo

This will create a drupal_cms_foo directory with a composer.json all set up with the basics, and properly linked into the rest of the project.