Chore: Move user errors to user service (#52460)

* Move user not found err to user service

* User ErrCaseInsensitive from user pkg

* User ErrUserAlreadyExists from user pkg

* User ErrLastGrafanaAdmin from user pkg

* Remove errors from model

pkg/middleware/middleware_jwt_auth_test.go

@@ -9,6 +9,7 @@ import (
 
 	"github.com/grafana/grafana/pkg/models"
 	"github.com/grafana/grafana/pkg/services/contexthandler"
+	"github.com/grafana/grafana/pkg/services/user"
 	"github.com/grafana/grafana/pkg/setting"
 )
 
@@ -88,7 +89,7 @@ func TestMiddlewareJWTAuth(t *testing.T) {
 				"foo-email": myEmail,
 			}, nil
 		}
-		sc.mockSQLStore.ExpectedError = models.ErrUserNotFound
+		sc.mockSQLStore.ExpectedError = user.ErrUserNotFound
 
 		sc.fakeReq("GET", "/").withJWTAuthHeader(token).exec()
 		assert.Equal(t, verifiedToken, token)