Improve danger/specs/Dangerfile by not requiring new specs if specific labels are applied

Signed-off-by: Rémy Coutable <remy@rymai.me>

danger/specs/Dangerfile

+NO_SPECS_LABELS = %w[backstage Documentation QA].freeze
 NO_NEW_SPEC_MESSAGE = <<~MSG.freeze
 You've made some app changes, but didn't add any tests.
 That's OK as long as you're refactoring existing code,
-but please consider adding the ~backstage label in that case.
+but please consider adding any of the %<labels>s labels.
 MSG
 
+def presented_no_changelog_labels
+  NO_SPECS_LABELS.map { |label| "~#{label}" }.join(', ')
+end
+
 has_app_changes = !git.modified_files.grep(%r{\A(ee/)?(app|lib|db/(geo/)?(post_)?migrate)/}).empty?
-has_spec_changes = !git.modified_files.grep(/spec/).empty?
+has_spec_changes = !git.modified_files.grep(%r{\A(ee/)?spec/}).empty?
+new_specs_needed = (gitlab.mr_labels & NO_SPECS_LABELS).empty?
 
-if has_app_changes && !has_spec_changes
-  warn NO_NEW_SPEC_MESSAGE, sticky: false
+if has_app_changes && !has_spec_changes && new_specs_needed
+  warn format(NO_NEW_SPEC_MESSAGE, labels: presented_no_changelog_labels), sticky: false
 end