Add object description cop

[yaorlov]

@DmitryTsepelev I've implemented the ObjectDescription cop
I've tested this cop on my project and it works fine but requires some customizations (Exclude:) in .rubocop.yml.
For example, I have directories (spec/graphql and lib/graphql) that follow the same pattern as in the config/default.yml. Also, base classes like this should be excluded:

class Types::BaseUnion < GraphQL::Schema::Union
end

Please let me know what you think

[DmitryTsepelev]

Hi @yaorlov!

I've tested this cop on my project and it works fine but requires some customizations (Exclude:) in .rubocop.yml.
For example, I have directories (spec/graphql and lib/graphql) that follow the same pattern as in the config/default.yml.

In this case you can configure Patterns in your project's .rubocop.yml to add directories to be checked along with app/graphql.

Also, base classes like this should be excluded

Agreed, let's try to use Exclude option in the .default.yml for this cop (I guess we can check for base_*.rb pattern).

Also, please add yourself to the CHANGELOG.

[yaorlov]

@DmitryTsepelev I've added Exclude for base types and also for generated graphql schema. CHANGELOG was updated too.

[DmitryTsepelev]

LGTM, thanks!