Move Self-Managed Trial Specific Logic from Trial to Trials::SM Model

Problem

The Trial model today contains logic for both SaaS and Self-Managed trials, but there is an ongoing effort in https://gitlab.com/groups/gitlab-org/-/epics/17546+ to create new models for Trials::SaaS and Trials::SM. As we continue to work on [SM Cloud Licensing Trials] Iteration 1.2: Upda... (&16047 - closed) and add more Self-Managed specific logic to the Trial model (ex: create_cloud_activation and cloud_activation), it may be worth exploring moving this logic to Trials::SM instead for better separation of concerns.

Proposal

Consider moving any Self-Managed specific logic from the Trial model to the new Trials::SM model (to be added in https://gitlab.com/gitlab-org/customers-gitlab-com/-/issues/13353)

Update usages throughout the code that referenced this logic in Trial to use the Trials::SM model instead