Fix keyword argument forwarding in Initializer module

[bolshakov]

The Initializer module's initialize method only captured positional arguments (*args), causing it to fail when containers were initialized with keyword arguments:

class MyContainer
  include Dry::Container::Mixin

  def initialize(config:, data_store:)
    # ...
  end
end

MyContainer.new(config: cfg, data_store: ds)

I updated Initializer#initialize to explicitly capture and forward keyword arguments using **kwargs:

def initialize(*args, **kwargs, &block)
  @_container = ::Concurrent::Hash.new
  super
end