New package signing key

Hello,

if you are installing Zato directly under Ubuntu - rather than using Docker Quickstart - then you may want to check the newest, slightly changed installation instructions.

Specifically, there is a new key to use and the command to use it is different because that is needed under Ubuntu 22.04 or newer.

https://zato.io/en/docs/3.2/admin/guide/install/ubuntu.html

Once more, if you use Docker Quickstart then you do not need to change anything.

Regards.