docs: Move and update dedicated instrumentor sandbox documentation
Documentation refresh as part of wrap-up for epic gitlab-com/gl-infra&1150 (closed).
The dedicated overview doc was getting bloated. Since we're adding more to the (instrumentor) sandbox documentation, this MR is to:
- Move the 'sandbox setup' section from 'dedicated overview' document to its separate file
- Add sections on
- general guideline for failing jobs
- upgrading using Auto-Deploy release versions and
- testing zero-downtime upgrades (ZDU)