Rails 5.2 upgrade cleanup

This is a followup to THREESCALE-6316

• check for deprecation messages in production log related to accessing configuration with string keys rails#35198
• remove protected_attributes gem and revisit all `#params#permit!` usages
• replace paperclip with ActiveStorage or update to the new project THREESCALE-8506
• [PARTIAL] remove dali and use standard functionality (new versions are unsupported on Ruby < 2.6 so we monkey patched)
• go through comments on https://github.com/3scale/porta/pull/2981 to clean-up