We are currently focused on adding other functionalities to the Bitnami catalog and the current applications on it. You can propose OSTicket to be added in the future using the link below
Unfortunately, we do have an ETA of when we will be adding new applications.
As an alternative, you can manually install it on top of the Bitnami LAMP Stack using the guide below
Please note that in case you find issues trying to configure the application, you will need to ask for help in the OSTicket official forums