We are currently building setup scripts for an unattended SDL Sites 9.1 installation.
The installer provides a series of switches to enable/disable certain functionality, as described here https://docs.sdl.com/LiveContent/content/en-US/SDL%20Tridion%20Sites-v2/GUID-B9FFD1EC-A598-42C7-92BF-C24D9B21B473
Unfortunately, I couldn't find an option to enable/configure the Add-On service this way. It is possible to configure this via the regular installation wizard.
Is this possible through the unattended install?