feat: active gitaly node disk space saturation
This adds a saturation point to monitor the amount of disk space that is available for receiving new repositories
We're using the sum of all the disks of nodes with more than 20% available disk space as a proxy for the number of active nodes. We want the total available space of nodes with more than 20% available to be at least 10% of the total space.
This would mean that we want approximately 10% of gitaly nodes to receive new traffic.
Current state: about 92% utilized. This is in line with what I was observing in https://gitlab.com/gitlab-com/gl-infra/capacity-planning/-/issues/40#note_1081078345
Edited by Bob Van Landuyt