We attempted to revert the rename of the `template` to `instance` column
in the `services` table in
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/24857 and
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/24885, but for
some installations (e.g. staging), the `template` column had been
dropped already because post-deploy migrations had finished.

We never actually shipped this change to production, but for these
environments we need to re-add the `template` column back into the table
or project creation will fail.

Note we do not do a data migration (e.g. set the `template` column to
true for rows that have a NULL `project_id`) for two reasons:

1. We don't want to insert a template by accident.
2. This rename only finished on development/staging environments.

Note that this migration happens in a post-deploy migration to ensure
`20200211152410_remove_instance_from_services.rb` gets a chance
to undo the migration first.