Add column_name to batched_background_migrations Admin API

lib/api/entities/batched_background_migration.rb

@@ -6,6 +6,7 @@ class BatchedBackgroundMigration < Grape::Entity
       expose :id, documentation: { type: :string, example: "1234" }
       expose :job_class_name, documentation: { type: :string, example: "CopyColumnUsingBackgroundMigrationJob" }
       expose :table_name, documentation: { type: :string, example: "events" }
+      expose :column_name, documentation: { type: :string, example: "id" }
       expose :status_name, as: :status, override: true, documentation: { type: :string, example: "active" }
       expose :progress, documentation: { type: :float, example: 50 }
       expose :created_at, documentation: { type: :dateTime, example: "2022-11-28T16:26:39+02:00" }

spec/requests/api/admin/batched_background_migrations_spec.rb

@@ -100,6 +100,7 @@
           expect(json_response.first['id']).to eq(migration.id)
           expect(json_response.first['job_class_name']).to eq(migration.job_class_name)
           expect(json_response.first['table_name']).to eq(migration.table_name)
+          expect(json_response.first['column_name']).to eq(migration.column_name)
           expect(json_response.first['status']).to eq(migration.status_name.to_s)
           expect(json_response.first['progress']).to be_zero
         end
@@ -151,6 +152,7 @@
               expect(json_response.first['id']).to eq(ci_database_migration.id)
               expect(json_response.first['job_class_name']).to eq(ci_database_migration.job_class_name)
               expect(json_response.first['table_name']).to eq(ci_database_migration.table_name)
+              expect(json_response.first['column_name']).to eq(ci_database_migration.column_name)
               expect(json_response.first['status']).to eq(ci_database_migration.status_name.to_s)
               expect(json_response.first['progress']).to be_zero
             end