Expose SPP instance-level setting in Application Settings API

Overview

As we built out Secret Push Protection and took it through an experimental and beta phases, we had a number of gaps in our API support for the feature. We want to address one of those gaps by exposing the secret push protection instance-level setting in the Application Settings API.

Please see this thread for further information.

Proposal

To address this gap, one could possibly:

• Expose pre_receive_secret_detection_enabled attribute in EE::API::Entities::ApplicationSetting.
• Update corresponding tests to ensure this works as expected, and is only displayed when the feature is licensed.
• Update corresponding API endpoint documentation to indicate this setting is only available for Ultimate.
• Update list of settings accessable via API in documentation to include the setting.