Add ActiveRecord::Base.connected_to?

[jhawthorn]

This can be used to check the currently connected role. It's meant to mirror ActiveRecord::Base.connected_to introduced in #34052

Usage:

ActiveRecord::Base.connected_to(role: :writing) do
  ActiveRecord::Base.connected_to?(role: :writing) #=> true
  ActiveRecord::Base.connected_to?(role: :reading) #=> false
end

cc @eileencodes

[eileencodes]

Looks great! Will merge once tests are green.

[eileencodes]

Sign codeclimate. We use assert_not over refute, can you update? https://codeclimate.com/github/rails/rails/pull/34680

[rafaelfranca]

Is this a public API method? If yes, it needs to be documented.