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/services/user/model.go

@@ -1,11 +1,21 @@
 package user
 
 import (
+	"errors"
 	"time"
 )
 
 type HelpFlags1 uint64
 
+// Typed errors
+var (
+	ErrCaseInsensitive   = errors.New("case insensitive conflict")
+	ErrUserNotFound      = errors.New("user not found")
+	ErrUserAlreadyExists = errors.New("user already exists")
+	ErrLastGrafanaAdmin  = errors.New("cannot remove last grafana admin")
+	ErrProtectedUser     = errors.New("cannot adopt protected user")
+)
+
 type User struct {
 	ID            int64 `xorm:"pk autoincr 'id'"`
 	Version       int