Support job token auth for read-only changelog generation API

What does this MR do and why?

Support job token auth for read-only changelog generation API

This change set adds support that allows authentication via CI_JOB_TOKEN for the read-only (GET) Changelog generation API. This is super useful to generate a changelog or release notes without any additional tokens.

Since this is a read-only endpoint the security impact is very low.

Changelog: added