Only initialize the admin service if necessary

[sagikazarmark]

Preflight Checklist

• I agree to follow the Code of Conduct that this project adheres to.
• I have searched the issue tracker for an issue that matches the one I want to file, without success.
• I am not looking for support or already pursued the available support channels without success.

Version

2.34.0

Storage Type

In-memory

Installation Type

Official container image, Official Helm chart

Expected Behavior

Improper configuration of admin service does not lead to errors when the admin service is not used at all.

Actual Behavior

Since 2.34.0 if a service account is not configured, the admin service falls back to default credentials. This causes problems on GKE: #2676

Steps To Reproduce

No response

Additional Information

When the groups scope is present AND admin service is not configured properly, Dex <2.34 fails anyway (I believe it may even panic), so not restoring prior behavior completely should be okay.

Proposed solution: when the groups scope is present, initialize the admin service with whatever configuration is present.

Correction, Dex opts to not fetch the groups in this case.

Configuration

No response

Logs

No response