Add docs about rotated signing keys for Gitaly
What does this MR do and why?
Signing key rotation has been added a while ago: gitaly@b87326c2
This MR adds the missing documentation.
The 17.0 major release is coming on May 16, 2024! This version brings many exciting improvements to GitLab, but also removes some deprecated features. We are introducing three breaking change windows during which we expect breaking changes to be deployed to GitLab.com. You can read more about it on our blogpost. The second breaking change window begins 2024-04-29 09:00 UTC and ends 2024-05-01 22:00 UTC.
Signing key rotation has been added a while ago: gitaly@b87326c2
This MR adds the missing documentation.