Load test using higher concurrent users

Summary

As part of determining the correct resource requests to put in place, we previously did some load testing, documented here: https://gitlab.com/charts/gitlab/blob/master/doc/architecture/resource-usage.md

Were several of the tests using concurrent users of around 100.

We should do another round of tests and look at a larger number of users, like 1000

This is a request that came in today from a customer who is looking to deploy this with that many active users, and would like us to have done some testing with those types of numbers first.

Before doing this we need to tackle https://gitlab.com/charts/gitlab/issues/1082