Make gitea webhooks openproject compatible (#28435)

This PR adds some fields to the gitea webhook payload that
[openproject](https://www.openproject.org/) expects to exists in order
to process the webhooks.
These fields do exists in Github's webhook payload so adding them makes
Gitea's native webhook more compatible towards Github's.

modules/structs/user.go

@@ -28,6 +28,8 @@ type User struct {
 	Email string `json:"email"`
 	// URL to the user's avatar
 	AvatarURL string `json:"avatar_url"`
+	// URL to the user's gitea page
+	HTMLURL string `json:"html_url"`
 	// User locale
 	Language string `json:"language"`
 	// Is the user an administrator