Include login_name in adminCreateUser response (#20283)

`login_name` (Authentication Sign-in Name) is not included in the response of `adminUserCreate` API. 
This PR is to return user-specified `login_name` if there is one.

modules/convert/user.go

@@ -73,6 +73,7 @@ func toUser(user *user_model.User, signed, authed bool) *api.User {
 	// only site admin will get these information and possibly user himself
 	if authed {
 		result.IsAdmin = user.IsAdmin
+		result.LoginName = user.LoginName
 		result.LastLogin = user.LastLoginUnix.AsTime()
 		result.Language = user.Language
 		result.IsActive = user.IsActive

modules/structs/user.go

@@ -17,6 +17,9 @@ type User struct {
 	ID int64 `json:"id"`
 	// the user's username
 	UserName string `json:"login"`
+	// the user's authentication sign-in name.
+	// default: empty
+	LoginName string `json:"login_name"`
 	// the user's full name
 	FullName string `json:"full_name"`
 	// swagger:strfmt email

templates/swagger/v1_json.tmpl

@@ -18487,6 +18487,12 @@
           "type": "string",
           "x-go-name": "UserName"
         },
+        "login_name": {
+          "description": "the user's authentication sign-in name.",
+          "type": "string",
+          "default": "empty",
+          "x-go-name": "LoginName"
+        },
         "prohibit_login": {
           "description": "Is user login prohibited",
           "type": "boolean",