feat: organization settings for user uniqueness (#10246)

# Which Problems Are Solved

Currently the username uniqueness is on instance level, we want to
achieve a way to set it at organization level.

# How the Problems Are Solved

Addition of endpoints and a resource on organization level, where this
setting can be managed. If nothing it set, the uniqueness is expected to
be at instance level, where only users with instance permissions should
be able to change this setting.

# Additional Changes

None

# Additional Context

Includes #10086
Closes #9964 

---------

Co-authored-by: Marco A. <marco@zitadel.com>

internal/domain/permission.go

@@ -65,6 +65,9 @@ const (
 	PermissionUserGrantWrite           = "user.grant.write"
 	PermissionUserGrantRead            = "user.grant.read"
 	PermissionUserGrantDelete          = "user.grant.delete"
+	PermissionIAMPolicyWrite           = "iam.policy.write"
+	PermissionIAMPolicyDelete          = "iam.policy.delete"
+	PermissionPolicyRead               = "policy.read"
 )
 
 // ProjectPermissionCheck is used as a check for preconditions dependent on application, project, user resourceowner and usergrants.