Workload analysis on GitLab.com - first iteration

In this issue, the goal is to analyze the database workload on GitLab.com and draw first conclusions from it. The idea is to uncover areas of interest. These would lend themselves as a focus for our group to improve database scalability.

1. Identify 2 areas of the application that have a high impact on the database
2. Explain how we define "high impact" in each of those cases
3. Document how we reached that conclusion
4. Create issues for each area and describe what causes the high database impact in this area (problem description)

As a deliverable, the results can go into a page on the handbook as a summary: https://about.gitlab.com/handbook/engineering/development/enablement/database/#documentation