Add a REST API endpoint to soft-delete an organization

The endpoint is DELETE POST /organizations/:id and calls Organizations::SoftDeleteService introduced in Rename deletion_scheduled state to soft_deleted... (!235915 - merged) • Rémy Coutable • 19.1 & Add Organizations::HardDeleteService and HardDe... (!238553 - merged) • Rémy Coutable • 19.1.

The corresponding GraphQL implementation is tracked at Add OrganizationDelete GraphQL mutation and exp... (#594313 - closed) • Jeaeun Kim • 19.1 • On track and implemented by Add OrganizationDelete GraphQL mutation and exp... (!235248 - merged) • Jeaeun Kim • 19.1.