Introduce an optional expiration date for SSH keys

Problem to Solve

Similar to #118893 (closed), GitLab customers don't have a way to enforce credential rotation within their environments. This is primarily due to a lack of a setting for Users to specify an expiration date when creating an SSH key.

Without the ability to set an expiration date, users, group owners, and administrators cannot adequately track or enforce credential rotation.

Additional Details

This MVC will set the groundwork for adding more comprehensive credential management to the GitLab application.

Proposal

Allow Users to specify an optional expiration date for SSH keys.