Add Middleware Read-Only api-user

[phavekes]

This issue is imported from pivotal - Originaly created at Oct 12, 2021 by Peter Havekes

Add a API user with read-only access to all API-endpoints, for use with internal scripting
https://github.com/OpenConext/Stepup-Middleware/blob/develop/config/packages/security.yaml

[phavekes]

Would be excellent so we can relate vetted tokens in SSID with stepup users in the legagy platform through some simple scripting. (Thijs Kinkhorst - Oct 12, 2021)