Link to maintained identity provider (#21015)

Author: MisinformedDNA

src/Identity/README.md

@@ -22,6 +22,6 @@ The previous versions of Identity for MVC5 and lower, previously available on Co
  * [ASP.NET Identity Cassandra Provider](https://github.com/lkubis/AspNetCore.Identity.Cassandra)
  * [ASP.NET Identity Firebase Provider](https://github.com/aguacongas/Identity.Firebase)
  * [ASP.NET Identity Redis Provider](https://github.com/aguacongas/Identity.Redis)
- * [ASP.NET Identity DocumentDB](https://github.com/FelschR/AspNetCore.Identity.DocumentDB)
+ * [ASP.NET Identity DocumentDB](https://github.com/codekoenig/AspNetCore.Identity.DocumentDb)
  * [ASP.NET Identity Amazon Cognito Provider](https://github.com/aws/aws-aspnet-cognito-identity-provider)
  * [ASP.NET Identity Marten Provider](https://github.com/yetanotherchris/Marten.AspNetIdentity)