Adjust sync_seat_link action to respond with JSON

This allows the FE to leverage async actions instead of a full page
refresh.

ee/app/controllers/admin/licenses_controller.rb

@@ -59,15 +59,15 @@ class Admin::LicensesController < Admin::ApplicationController
   end
 
   def sync_seat_link
-    sync_result = Gitlab::SeatLinkData.new.sync
-
-    if sync_result
-      flash[:notice] = _('Your license was successfully synced.')
+    respond_to do |format|
+      format.json do
+        if Gitlab::SeatLinkData.new.sync
+          render json: { success: true }
         else
-      flash[:error] = _('There was an error when trying to sync your license. Please verify that your instance is using an active license key.')
+          render json: { success: false }, status: :unprocessable_entity
+        end
+      end
     end
-
-    redirect_to admin_license_path
   end
 
   private

ee/spec/controllers/admin/licenses_controller_spec.rb

@@ -115,22 +115,22 @@ RSpec.describe Admin::LicensesController do
     context 'with seat link enabled' do
       let(:seat_link_enabled) { true }
 
-      it 'redirects with a successful message' do
-        post :sync_seat_link
+      it 'returns a success response' do
+        post :sync_seat_link, format: :json
 
-        expect(response).to redirect_to(admin_license_path)
-        expect(flash[:notice]).to eq('Your license was successfully synced.')
+        expect(response).to have_gitlab_http_status(:ok)
+        expect(json_response).to eq({ 'success' => true })
       end
     end
 
     context 'with seat link disabled' do
       let(:seat_link_enabled) { false }
 
-      it 'redirects with an error message' do
-        post :sync_seat_link
+      it 'returns a failure response' do
+        post :sync_seat_link, format: :json
 
-        expect(response).to redirect_to(admin_license_path)
-        expect(flash[:error]).to match('There was an error when trying to sync your license.')
+        expect(response).to have_gitlab_http_status(:unprocessable_entity)
+        expect(json_response).to eq({ 'success' => false })
       end
     end
   end

locale/gitlab.pot

@@ -31914,9 +31914,6 @@ msgstr ""
 msgid "There was an error when subscribing to this label."
 msgstr ""
 
-msgid "There was an error when trying to sync your license. Please verify that your instance is using an active license key."
-msgstr ""
-
 msgid "There was an error when unsubscribing from this label."
 msgstr ""
 
@@ -36549,9 +36546,6 @@ msgstr ""
 msgid "Your license is valid from"
 msgstr ""
 
-msgid "Your license was successfully synced."
-msgstr ""
-
 msgid "Your license will be included in your GitLab backup and will survive upgrades, so in normal usage you should never need to re-upload your %{code_open}.gitlab-license%{code_close} file."
 msgstr ""