Authn: Prevent empty username and email during sync (#76330)

* Move errors to error file

* Move check for both empty username and email to user service

* Move check for empty email and username to user service Update

* Wrap inner error

* Set username in test

pkg/services/user/error.go

@@ -0,0 +1,24 @@
+package user
+
+import (
+	"errors"
+
+	"github.com/grafana/grafana/pkg/util/errutil"
+)
+
+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")
+	ErrNoUniqueID        = errors.New("identifying id not found")
+	ErrLastSeenUpToDate  = errors.New("last seen is already up to date")
+	ErrUpdateInvalidID   = errors.New("unable to update invalid id")
+)
+
+var (
+	ErrEmptyUsernameAndEmail = errutil.BadRequest(
+		"user.empty-username-and-email", errutil.WithPublicMessage("Need to specify either username or email"),
+	)
+)