Expired SaaS subscriptions should revert to free plan.
## Summary
When a SaaS subscription expires, there is no job which deprovisions the paid plan from the GitLab.com namespace.
## Actions
1. [x] Create a job which converts the plan associated with the namespace in GitLab.com to free for newly expired SaaS subscriptions (s/b daily cadence) https://gitlab.com/gitlab-org/customers-gitlab-com/-/issues/2101
1. [x] Implement a retry service for failed downgrades https://gitlab.com/gitlab-org/customers-gitlab-com/-/issues/2102
1. [x] Implement logging of failed downgrades (in a reporting consumable way for manual next steps) https://gitlab.com/gitlab-org/customers-gitlab-com/-/issues/2103
1. [x] Spike: Identify top core issues causing failures; create applicable issues https://gitlab.com/gitlab-org/customers-gitlab-com/-/issues/2104
1. [ ] Placeholder to resolve core issues preventing deprovisioning job success
1. [x] Clean-up existing data and downgrade outstanding expired namespaces https://gitlab.com/gitlab-org/customers-gitlab-com/-/issues/2105
1. [x] Investigate renewals behavior https://gitlab.com/groups/gitlab-org/-/epics/4297
1. [x] Document SaaS Deprovisioning (technical) processes https://gitlab.com/gitlab-org/customers-gitlab-com/-/issues/2920
epic