Rescue DB connection error.

[DanielePalombo]

Summary

If the DB connection fails, the initializer shouldn't raise any error.

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[kennyadsl]

@DanielePalombo why should fail when the DB adapter is not present?

[DanielePalombo]

@kennyadsl My fault.

This PR aims to do exactly the opposite! The initializer should not fail if the DB connection fails.

I'm updating the PR and commit description

[elia]

I think rescuing without letting the user know might hide some issues, I suggested a could have alternatives that might work.

Of course if there's no other option we can add this

[elia]

@DanielePalombo since Solidus v3.3 static model prefs can be added passing a string for the class name.

I think at least for the first configuration it can be done that way:

Spree::Config.static_model_preferences.add(
  'SolidusBolt::PaymentMethod',
  'bolt_credentials',
  ::SolidusBolt::Engine.bolt_credentials_hash
)

The second one is more tricky because it needs the database, thoughts on using ActiveRecord::Base.connected? or even specifically SolidusBolt::BoltConfiguration.connected??