[Rails5] Update `type_cast_*_database` methods

What does this MR do?

In Rails 5.0 two type cast methods have been renamed:

1. The type_cast_for_database method has been renamed to serialize.
2. The type_cast_from_database method has been renamed to deserialize.

This MR adds support of the renamed methods for Rails 5.

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)