Move product error budget dashboards out of the current folder

Currently, the autogenerated error budget dashboards for the product stage (eg https://gitlab.com/gitlab-com/runbooks/-/blob/master/dashboards/product/create_error_budget.dashboard.jsonnet) resides in the dashboards/product folder where other manual dashboards like create.dashboard.jsonnet is there.

This folder is protected, so they are not subject to automatic deletion when the dashboards have not been updated for more than 7 days.

As a result, some removed dashboards from the source code (example) won't get cleaned up. These autogenerated dashboards get deleted when we do regular update feature categories (like in this MR).

We should move these autogenerated error budget dashboards to another folder so they are subject to deletion.

This was brought to light from #3564 (comment 1963992405)