feat: Add without_instance_methods qualifier to enum matcher

[vaot]

Add a without_instance_methods qualifier to enum matcher.

class Issue < ActiveRecord::Base
  enum status: [:open, :closed], instance_methods: false
end

RSpec.describe Issue, type: :model do
  it do
    should define_enum_for(:status).
      without_instance_methods
  end
end

[vaot]

Hey @matsales28 👋 , do you have any thoughts on this one ? Thank you.

[matsales28]

Hey @matsales28 👋 , do you have any thoughts on this one ? Thank you.

Hey @vaot, hope you're doing great. I'm currently on vacation for the next two weeks. Planning on catching up the PRs for shoulda-matchers after that.