Add data migration for attribute default values.

On certain instances of the Open Build Service the default
attribute values got lost, since they are only created once
at the first setup by the seeds. This causes failing validations
when creating certain attribute, since they rely on the default values.

Fixes #8143

src/api/db/data/20190902110039_add_attribute_default_values.rb

@@ -0,0 +1,16 @@
+class AddAttributeDefaultValues < ActiveRecord::Migration[5.2]
+  def up
+    ans = AttribNamespace.where(name: 'OBS').first
+    return unless ans
+
+    at = ans.attrib_types.where(name: 'QualityCategory').first
+    at.default_values.where(value: 'Development', position: 1).first_or_create if at
+
+    at = ans.attrib_types.where(name: 'MaintenanceIdTemplate').first
+    at.default_values.where(value: '%Y-%C', position: 1).first_or_create if at
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
+end

src/api/db/data_schema.rb

@@ -1,2 +1,2 @@
 # encoding: UTF-8
-DataMigrate::Data.define(version: 20190228170655)
+DataMigrate::Data.define(version: 20190902110039)