[Rails5] Add FALSE_VALUES constant to Service#boolean_accessor

What does this MR do?

In Rails 5.0 the ActiveRecord::ConnectionAdapters::Column::TRUE_VALUES constant has been removed and the remaining FALSE_VALUES constant has been moved to ActiveModel::Type::Boolean.

This MR adds the ActiveModel::Type::Boolean::FALSE_VALUES constant to let Service#boolean_accessor work in Rails 5.0.

Are there points in the code the reviewer needs to double check?

No.

Why was this MR needed?

Migration to Rails 5.0

Screenshots (if relevant)

No.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

#14286 (closed) and !12841 (closed)