AddGitlabInstanceAdministrationProject migration won't run on new instances

This relates to https://gitlab.com/charts/gitlab/issues/1550.

New instances don't run migrations (i.e. they init from db/schema.rb and stop), so migrations such as 20190801072937_add_gitlab_instance_administration_project.rb won't actually do anything.

Besides, it also seems to go against using ActiveRecord (and running application code) inside migrations.

Should we consider:

1. Lazily initializing the project when needed
2. Removing this migration

/cc: @rpereira2