Update GameSDK RelationshipsManager to indicate that OAuth is now required

[bremea]

Fixes this issue.

The GameSDK Relationships Manager recently received a breaking change to the OnRefresh callback. After reaching out to developer support, it was confirmed that this callback now requires the target user to authenticate with OAuth2 and accept the relationships.read scope (which requires Discord approval). PR adds a warning above the OnRefresh documentation indicating that the scope is now required for the callback to function properly.