Add foreign keys and an index to StructuredError(Attributes)

These changes will ensure a better data consistency and faster access. We further ensure that records should be deleted properly.

db/migrate/20230320220011_add_foreign_keys_to_structured_errors.rb

@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+class AddForeignKeysToStructuredErrors < ActiveRecord::Migration[7.0]
+  def change
+    add_foreign_key :structured_errors, :submissions
+    add_foreign_key :structured_errors, :error_templates
+  end
+end

db/migrate/20230320220012_add_foreign_keys_and_index_to_structured_error_attributes.rb

@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+class AddForeignKeysAndIndexToStructuredErrorAttributes < ActiveRecord::Migration[7.0]
+  def change
+    add_foreign_key :structured_error_attributes, :structured_errors
+    add_foreign_key :structured_error_attributes, :error_template_attributes
+    add_index :structured_error_attributes, :structured_error_id
+  end
+end