Add Capybara which was extracted from rubocop-rspec

In version rubocop-rspec 3.x cop departments are extracted to another gem
(Capybara, FactoryBot, Rails)
https://docs.rubocop.org/rubocop-rspec/upgrade_to_version_3.html

The comment is split out to appease "Missing comment/explanation for Cop"
warning.

config/capybara.yml

@@ -1,5 +1,11 @@
+require: rubocop-capybara
+
 # Within GOV.UK we use Capybara test method syntax of feature,
-# scenario. We don't want this outside of feature or system specs though.
+# scenario. 
+Capybara:
+  Enabled: true
+
+# We don't want this cop outside of feature or system specs though.
 RSpec/Dialect:
   Exclude:
     - 'spec/features/**/*.rb'

rubocop-govuk.gemspec

@@ -17,6 +17,7 @@ Gem::Specification.new do |spec|
 
   spec.add_dependency "rubocop", "1.64.1"
   spec.add_dependency "rubocop-ast", "1.31.3"
+  spec.add_dependency "rubocop-capybara", "2.21.0"
   spec.add_dependency "rubocop-rails", "2.25.0"
   spec.add_dependency "rubocop-rake", "0.6.0"
   spec.add_dependency "rubocop-rspec", "3.0.1"