Implement DELETE /users/{user_id endpoint for APIv4 - rebase cleanup (#5307)

* added delete user endpoint

* added unit test for delete user endpoint

* added delete user driver

api4/user_test.go

@@ -219,6 +219,37 @@ func TestUpdateUser(t *testing.T) {
 	CheckNoError(t, resp)
 }
 
+func TestDeleteUser(t *testing.T) {
+	th := Setup().InitBasic().InitSystemAdmin()
+	Client := th.Client
+	
+	user := th.BasicUser
+	th.LoginBasic()
+
+	testUser := th.SystemAdminUser
+	_, resp := Client.DeleteUser(testUser.Id)
+	CheckForbiddenStatus(t, resp)
+
+	Client.Logout()
+	
+	_, resp = Client.DeleteUser(user.Id)
+	CheckUnauthorizedStatus(t, resp)
+
+	Client.Login(testUser.Email, testUser.Password)
+
+	user.Id = model.NewId()
+	_, resp = Client.DeleteUser(user.Id)
+	CheckNotFoundStatus(t, resp)
+
+	user.Id = "junk"
+	_, resp = Client.DeleteUser(user.Id)
+	CheckBadRequestStatus(t, resp)
+
+	_, resp = Client.DeleteUser(testUser.Id)
+	CheckNoError(t, resp)
+
+}
+
 func TestUpdateUserRoles(t *testing.T) {
 	th := Setup().InitBasic().InitSystemAdmin()
 	Client := th.Client