Generate Site Details more frequently

As part of the project to obtain Site Details from all VIP sites (to gather data such as the enabled plugins and their versions, Jetpack status, VIP search status…), we are now increasing the frequency of generation, from 4 hours to 30 minutes.

This will allow us to fetch data in a more reliable and predictable way while we keep developing the project.

https://github.com/Automattic/vip-go-mu-plugins/pull/1944