Fixes #30862 - introduce SettingRegistry (#8002)

SettingRegistry keeps all the setting information as set of SettingPresenters in memory.
This registry should be the public API for accessing setting values and keeps all the information about settings.
That will allow dropping all information except `name` and `value` from database.

The public interface should be:
`Foreman.settings[<name>] => value` with syntactic suggar `Setting[<name>]` proxying to this method.

We load values from database per request and repopulate the values, what is quite fast. This allows us dropping the cache for setting.

• Initialize the registry manually at specific moment and note if the registry is
  ready or not by `ready?` method.
• Reload values by `Foreman.setting.load_values` before every request
• Disables validations on Setting default values creation as those come from code and thus should be always valid, also this creation will be dropped in the future

Refs #30862 - do not validate new settings

While creating the settings, the definitions are not loaded yet, so the
validations depending on other setting values are failing. We should not
validate on create anyway.

This is fixing a forgotten validation on new setting from 8137b14c.