Add OIDC Documentation for OneLogin

[rh0dy]

Description

This is to add an example of configuring OpenID Connect with OneLogin, a popular Identity Provider. After quite some time fiddling around, I found a setup that works well for team and user synchronisation (notably using Semicolon Delimited Input (Multi-value output) for the OIDC groups values), so wanted to share it to help others.

Addressed Issue

N/A

Additional Details

N/A

Checklist

• I have read and understand the contributing guidelines
• This PR fixes a defect, and I have provided tests to verify that the fix is effective
• This PR implements an enhancement, and I have provided tests to verify that it works as intended
• This PR introduces changes to the database model, and I have added corresponding update logic
• This PR introduces new or alters existing behavior, and I have updated the documentation accordingly

[nscuro]

Thanks @rh0dy, much appreciated!