Update to Rails 7.2

[olleolleolle]

This PR upgrades the configuration to Rails 7.2 configuration.

I attempted to keep close to what Rails outputs, so that the update to the next version of Rails is not so difficult.

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In order to deploy this:

• Be on Rails 7.1 defaults in the production deployed app
• Get to Rails 7.1 in cache settings in deployed app
• Fix Warnings:

DEPRECATION WARNING: `Rails.application.config.active_record.allow_deprecated_singular_associations_name` is deprecated and will be removed in Rails 8.0. (called from <top (required)> at /Users/olle.jonsson/opensource/planner/config/environment.rb:5)
DEPRECATION WARNING: `Rails.application.config.active_record.commit_transaction_on_non_local_return` is deprecated and will be removed in Rails 8.0. (called from <top (required)> at /Users/olle.jonsson/opensource/planner/config/environment.rb:5)
DEPRECATION WARNING: Rails.application.config.active_job.use_big_decimal_serializer is deprecated and will be removed in Rails 8.0. (called from <top (required)> at /Users/olle.jonsson/opensource/planner/config/environment.rb:5)