Make endpoint for retrieving Service Ping payload accessible via PAT

Problem

General Problem laid out in &12251 (closed).

Desired Outcome

• API endpoint to retrieve last calculated Service Ping is available
• The endpoint can only be accessed with a PAT with the scope described in #435350 (closed)

Proposed Solution

Reuse the endpoint the endpoint provided in application_settings_controller.rb and make it accessible via the PAT from #435350 (closed)

How to verify

As an instance admin on a local GDK instance I can retrieve the last calculated Service Ping via a REST Endpoint with a PAT with the correct scope