fix: make "login_name" field optional for API edit user (#38917) (#38945)

Backport #38917

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

modules/structs/admin_user.go

@@ -11,7 +11,6 @@ type CreateUserOption struct {
 	// The authentication source ID to associate with the user
 	SourceID int64 `json:"source_id"`
 	// identifier of the user, provided by the external authenticator (if configured)
-	// default: empty
 	LoginName string `json:"login_name"`
 	// username of the user
 	// required: true
@@ -44,9 +43,7 @@ type EditUserOption struct {
 	// The authentication source ID to associate with the user
 	SourceID int64 `json:"source_id"`
 	// identifier of the user, provided by the external authenticator (if configured)
-	// default: empty
-	// required: true
-	LoginName string `json:"login_name" binding:"Required"`
+	LoginName *string `json:"login_name"`
 	// swagger:strfmt email
 	// The email address of the user
 	Email *string `json:"email" binding:"MaxSize(254)"`