Invalid config options for `oauth2-proxy-k8s` on channel `0.1/stable`

**Note: This issue was generated with AI assistance (GitHub Copilot) based on automated log analysis and triage.**
Filed by @canonical/solutions-qa

## Problem
Test execution for `oauth2-proxy-k8s` (channel 0.1/stable, revision 3) results in the `target` application entering a `blocked` state with the following message:

```
missing `upstream` config
```

The newer versions of this charm have different config options, so this only applies to channel `0.1/stable`. We need to create a test config for the charm

No file or test entry point is named. Start by locating the test configuration for oauth2-proxy-k8s on channel 0.1/stable at revision 3, then compare its options with the charm's required upstream setting; it is done when the target application no longer enters a blocked state for missing upstream config.

Written by the indexing model from the issue text.