Add silent_admin_exports_enabled setting
What does this MR do and why?
This adds a new application setting JSONB column uses the steps according to our development guide.
A second MR is making use of the setting !151278 (merged).
The setting is a silent mode for admin-initiated project and group file-based exports (even if the setting is enabled it will be a regular noisy export for non-admins https://gitlab.com/gitlab-org/gitlab/-/issues/294168).
MR acceptance checklist
Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.
Related to #294168
Edited by Luke Duncalfe