Cluster scoped users option #55

Pros:

• Users could be marked as owners for generated resources and claims via ownerReferences and deletion of user results in cleanup of their resources
• Permits easy cleanup of RedisClaims etc
• Makes it really easy to implement handling for GDPR requests

Cons:

• Complicates codebase if we were to keep namespace scoped users as well

Other:

• Discourages use of custom resources directly by applications because applications can't assume users are cluster or namespace scoped
• Paves way to NamespaceClaim, to automatically clean up namespaces/sandboxes created for the user
• Paves way to ServiceMailboxClaim, so Wildduck operator can pull mailbox claims from different namespaces and set up type: service users for them in first come, first serve manner
• Cluster scoped users make sense especially when Kube API is configured to authenticate with the same OIDC provider
• Makes it possible to include ownerReferences in an OIDC claim so applications that create resources on users behalf have easy way to add the reference, most notably that includes the Kubernetes uid of the user