feat: explain temporary SLOs to the on-call handover template

What

Add Temporary SLOs to the on-call handover, living alongside the lists of incidents.

Why

Live Demo: https://gitlab.com/gitlab-com/gl-infra/gitlab-dedicated/team/-/issues/10309

If there is a page for any one of these, the user impact is significantly worse than it is for tenants with similar alerts. One of these was paging through last week and was not actioned, it is really important that everyone is aware of these, so I'm placing them in several places.

See also: !656 (merged)