[MM-46694] A/B Test: welcome post (#20926)

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

app/user.go

@@ -209,6 +209,19 @@ func (a *App) IsFirstUserAccount() bool {
 	return a.ch.srv.platform.IsFirstUserAccount()
 }
 
+func (a *App) IsFirstAdmin(user *model.User) bool {
+	if !user.IsSystemAdmin() {
+		return false
+	}
+
+	adminID, err := a.Srv().Store().User().GetFirstSystemAdminID()
+	if err != nil {
+		return false
+	}
+
+	return adminID == user.Id
+}
+
 // CreateUser creates a user and sets several fields of the returned User struct to
 // their zero values.
 func (a *App) CreateUser(c request.CTX, user *model.User) (*model.User, *model.AppError) {