IAM: Add the implementation of the Update User API (#112054)

* wip

* Add validate, wire mutate, add tests

* Address copilot's feedback

* Address feedback

pkg/tests/apis/iam/testdata/user-test-create-2-v0.yaml

@@ -0,0 +1,11 @@
+apiVersion: iam.grafana.app/v0alpha1
+kind: User
+metadata:
+  namespace: default
+  name: user2
+spec:
+  email: testuser2@example.com
+  login: testuser2
+  name: Test User 2
+  provisioned: false
+  role: Viewer

pkg/tests/apis/iam/testdata/user-test-create-v0.yaml

@@ -8,4 +8,4 @@ spec:
   login: testuser1
   name: Test User 1
   provisioned: false
-  
+  role: None