don't override `Ability.ability_logic` on include

[no-reply]

Descriptive summary

When Hydra::Ability is included in a class, it overrides all existing ability_logic entries (at https://github.com/samvera/hydra-head/blob/master/hydra-access-controls/lib/hydra/ability.rb#L16). avoid this.

Rationale

Overriding existing ability logic entries silently removes important permissions behavior in the application. This unexpected behavior can occur for reasons as simple as including this module in the "wrong" order.

Expected behavior

class Ability
  self.ability_logic = [:my_custom_ability_hook, :other_ability_hook]
  include Hydra::Ability
end

Ability.ability_logic.include?(:my_custom_ability_hook) # => true

Actual behavior

Ability.ability_logic.include?(:my_custom_ability_hook) # => false

Steps to reproduce the behavior

the easiest way to realistically reproduce is to do something like

class Ability
  include Blacklight::AccessControls::Ability
  self.ability_logic = [:my_custom_ability_hook]
  # more logic here
  # ...
  # and so on
  include Hydra::Ability
end