Implement this as an EE feature (Ultimate)

Overview

As the pre-receive secret detection feature is introduced as an Ultimate-only feature (internal), we have to follow the guidelines to ensure it is treated as such. This is important from a licensing-point of view, and should not be skipped.

Please see parent epic for more details and considerations.

Implementation Plan

• Determine the feature identifier, e.g. pre_receive_secret_detection.
• Update GitlabSubscriptions::Features to add the feature identifer under ULTIMATE_FEATURES.
• Follow the guidelines to guard the new push check introduced in #427039 (closed).