Fixed issue where scope is nil when a param_group is used inside an array_of_hash

[joshio1]

When a param_group is used inside an array_of_hash and the param_group is in a different module / controller, the scope is set to nil, when the param_group is initialized.
This leads to this error:
apipie-rails/lib/apipie/dsl_definition.rb:379:in `param_group': undefined method `apipie_concern?' for nil:NilClass (NoMethodError)

Steps to reproduce:
In a different module define the following param_group:

module UsersSchema:

 module UsersSchema
   def self.included(klazz)
     klazz.def_param_group :index_users do
       property :response, Hash do
          property :users, array_of: Hash do
            param_group :extended_users_schema
          end
       end
     end
     klazz.def_param_group :extended_users_schema do
        property :id, Integer, :desc => 'ID of the user'
     end
   end
 end

The :extended_users_schema gets a scope of nil and a scope has to be explicitly passed to this param_group.

This PR is an attempt to avoid doing that and infer the scope based on the parent param's param_group.

[mathieujobin]

please add a test to reproduce the problem if you can 🙏

[mathieujobin]

merged in with #774

[mathieujobin]

released as v0.8.2