Added ability to add format to model attribute error key

[ygreeek]

I've added ability to add format to model attribute error key
What problem does it solve?
For example we have following locale.yaml:

company:
  attributes:
    provider:
      already_used_by_other_provider: "Already used by other provider"
      already_registered_by_another_provider: "already registered by another provider"

We want to show full_error of already_used_by_other_provider key as %{message}, but want the already_registered_by_another_provider error key as %{attribute} %{message}

This can now be achieved by declaring the format like this:

company:
  attributes:
    provider:
      already_used_by_other_provider: 
        message: "Already used by other provider"
        format: "%{message}"
      already_registered_by_another_provider: "already registered by another provider"