Expand the Devise unconfirmed message

Previously the Devise error message that was displayed to users with
un-confirmed email addresses was so brief that it confused users. This
expands the message to explain what the user should do next.

changelogs/unreleased/29279-add-resend-confirmation-link-to-login-failure-message.yml

+---
+title: Improve error message when unconfirmed user tries to log in
+merge_request: 34818
+author:
+type: changed

config/locales/devise.en.yml

@@ -15,7 +15,7 @@ en:
       not_found_in_database: "Invalid %{authentication_keys} or password."
       timeout: "Your session expired. Please sign in again to continue."
       unauthenticated: "You need to sign in or sign up before continuing."
-      unconfirmed: "You have to confirm your email address before continuing."
+      unconfirmed: "You have to confirm your email address before continuing. Please check your email for the link we sent you, or click 'Resend confirmation email'."
     mailer:
       confirmation_instructions:
         subject: "Confirmation instructions"

ee/spec/controllers/groups/group_members_controller_spec.rb

@@ -163,7 +163,7 @@ RSpec.describe Groups::GroupMembersController do
           post :request_access, params: { group_id: group }
 
           expect(response).to redirect_to(new_user_session_path)
-          expect(response).to set_flash.to 'You have to confirm your email address before continuing.'
+          expect(response).to set_flash.to I18n.t('devise.failure.unconfirmed')
           expect(group.requesters.exists?(user_id: requesting_user)).to be_falsey
           expect(group.users).not_to include requesting_user
         end

spec/features/users/login_spec.rb

@@ -110,7 +110,7 @@ RSpec.describe 'Login' do
 
         gitlab_sign_in(user)
 
-        expect(page).not_to have_content('You have to confirm your email address before continuing.')
+        expect(page).not_to have_content(I18n.t('devise.failure.unconfirmed'))
         expect(page).not_to have_link('Resend confirmation email', href: new_user_confirmation_path)
       end
     end
@@ -124,7 +124,7 @@ RSpec.describe 'Login' do
 
           gitlab_sign_in(user)
 
-          expect(page).to have_content('You have to confirm your email address before continuing.')
+          expect(page).to have_content(I18n.t('devise.failure.unconfirmed'))
           expect(page).to have_link('Resend confirmation email', href: new_user_confirmation_path)
         end
       end
@@ -820,7 +820,7 @@ RSpec.describe 'Login' do
           gitlab_sign_in(user)
 
           expect(current_path).to eq new_user_session_path
-          expect(page).to have_content('You have to confirm your email address before continuing.')
+          expect(page).to have_content(I18n.t('devise.failure.unconfirmed'))
         end
       end
     end