Review IOPS recommendations

We currently make a blanket recommendation for Gitaly in terms of disk IOPS - At least 8,000 input/output operations per second (IOPS) for read operations and 2,000 IOPS for write operations.

Being transparent this has been around for a long time and hasn't had much scrutiny in recent years. We know that it works but perhaps it's not required in all cases and doesn't allow for flexibility on smaller instances.

It's no mean feat to try and figure out what IOPS users should have on their usage shape but it may be perhaps still attempting anyways to ensure we're advising customers correctly. It's felt the Gitaly team would be best placed to advise on this.