Down-tier delayed deletion to core
## Goal
Extend the pending deletion state to all pricing tiers, including free tier projects and groups, creating a consistent experience throughout GitLab. This change will introduce a pending deletion period before permanent deletion for all entities.
### User Benefits
* Protection against accidental deletions for all users regardless of pricing tier
* Consistent experience when deleting items across the platform
* Opportunity to recover from mistaken deletions without support intervention
### GitLab Benefits
* Reduced support ticket volume for deletion recovery requests
* More consistent codebase with standardized deletion behavior
* Improved user satisfaction across all pricing tiers
## Requirements
* Database schema changes to track deletion state across all entity types
* Storage mechanism for preserving deleted content during the pending period
* Consistent deletion flow implementation for free tier projects and groups
* Backend logic to automatically transition from pending to permanent deletion
* Testing across all entity types and pricing tiers to ensure consistent behavior
* Pending deletion period for a namespace is dependent on the [instance setting](https://docs.gitlab.com/user/project/working_with_projects/#delayed-project-deletion):
* Ensure the instance setting is exposed for the free tier. If possible, set the default to 30 days for self-managed (or keep their existing selection). On SaaS, the default would be 7 days as per https://docs.gitlab.com/user/project/working_with_projects/#delayed-project-deletion. We will enhance it later to [30 days](https://gitlab.com/groups/gitlab-org/-/epics/17375).
* Ensure the instance setting covers free tier namespaces moving forward.
Related to: https://gitlab.com/gitlab-com/Product/-/issues/14057
epic