## Summary
In this pull request we're adding support for OIDC allowed groups in the
OSS version as part of work for
https://github.com/coder/coder/issues/17027.
### Changes
- Restored support for parsing group allow list in OSS code
### Testing
- Added tests for OSS code
- Tested allowed/prohibited group OIDC flows in premium and OSS
Adds a custom marshaler to handle some cases where nils were being
marshaled to nulls, causing the web UI to throw an error.
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Co-authored-by: Steven Masley <stevenmasley@gmail.com>