Change existing migration to create Category

Relevant ticket(s):

* https://mitlibraries.atlassian.net/browse/TCO-125

How does this address that need:

* Creates a Category "Flagged" if one does not already exist before
  trying to update data based on this specific Category

Document any side effects to this change:

* This migration has already run and it is normally not a good practice
  to update migrations to prevent databases from not bein in synch
  with the migration. In this case, all this does is introduce the code
  that was run manually in environments where this was run so it is
  fine and expected that those environments will not run it again.

db/migrate/20241204214748_change_column_null_confirmation_category.rb

@@ -1,5 +1,10 @@
 class ChangeColumnNullConfirmationCategory < ActiveRecord::Migration[7.1]
   def change
+    Category.find_or_create_by(
+      name: 'Flagged',
+      description: 'A search which has sensitive information that should be excluded from further processing.'
+    )
+
     change_column_null :confirmations, :category_id, false, Category.find_by(name: 'Flagged').id
   end
 end