www/rubygem-bullet_train-fields: Add rubygem-bullet_train-fields 1.7.2

Bullet Train includes a collection of view partials that are intended to DRY-up
as much redundant presentation logic as possible for different types of form
fields without taking on a third-party dependency like Formtastic.

These form field partials standardize and centralize the following behavior
across all form fields that use them:

• Apply theme styling and classes.
• Display any error messages for a specific field inline under the field itself.
• Display a stylized asterisk next to the label of fields that are known to be required.
• Any labels, placeholder values, and help text are defined in a standardized way in the model's localization Yaml file.
• For fields presenting a static list of options (e.g. a list of buttons or a select field) the options can be defined in the localization Yaml file.