Fix many_to_many when one of the models has a prefix to the intersection model association

[bguban]

Fix many_to_many when one of the models is under a namespace and has a prefix to the intersection model association.

class Hc::Validator < ApplicationRecord
has_many :validator_universes
has_many :universes, through: :validator_universes, inverse_of: :hc_validators
end

class Hc::ValidatorResource < ApplicationResource
many_to_many :universes, resource: UniverseResource, foreign_key: { hc_validator_universes: :validator_id }
end

class Hc::ValidatorUniverse < ApplicationRecord
belongs_to :validator
belongs_to :universe
end

class Universe < ApplicationRecord
has_many :hc_validator_universes, class_name: 'Hc::ValidatorUniverse'
has_many :hc_validators, class_name: 'Hc::Validator', through: :hc_validator_universes, source: :validator
end

class UniverseResource < ApplicationResource
many_to_many :hc_validators, resource: Hc::ValidatorResource, foreign_key: { validator_universes: :universe_id }
end

[jkeen]

@bguban Mind adding a test for this? I'm not quite understanding the issue