Prepare change procedure for Redis upgrade

Based on the results from https://gitlab.com/gitlab-com/gl-infra/infrastructure/-/issues/12451, we can design our upgrade procedure.

That will be a semi-automated checklist which we will use as a template for the change issue.

We can source from some of the prior art (source):

Once we have the procedure in place, we can use it to upgrade the first redis cluster in gstg (https://gitlab.com/gitlab-com/gl-infra/infrastructure/-/issues/12344).

Edited by Igor