Add a new terraform resource for creating a Super Admin user

[anna-geller]

Feature description

Ideal outcome:

• that user has permission to create roles, users, groups, and service accounts
• there can be multiple superadmin users created from terraform (even if it requires multiple terraform apply runs with the first one using the special initial endpoint and the following terraform apply runs being triggered after initialization with that first instance admin user credentials)
• allowing creating it in a way that all follow-up resources like tenant + namespace resources depend on one or more Instance Admin user resources