[EPIC] Proposed Integration: GitLab <> Confluence Cloud
### Description
GitLab has a huge amount of features, but some of them are available only through the Web UI. When dealing with automation and integration with other services, the lack of API may be a blocker. This is a major need for many users, as they need to be able to integrate GitLab with their existing tools and systems. While our work in ~"Category:Integrations" may support _some_ of those needs, supporting the rest can be done with robust API support.
### Proposal
1. Discuss product-wide coverage improvements here in this issue
1. Mark any individual issues that relate directly to expanding our existing APIs as ~"api:coverage"
1. Create a Periscope dashboard that groups the volume of traffic to API endpoints by stage
1. The ~"Category:APIs/SDKs" team will address issues not being picked up by the stage
### Confluence test instance
There is a test VM [`ecosystem-confluence-lab-1` in GCP](https://console.cloud.google.com/compute/instancesDetail/zones/us-central1-a/instances/ecosystem-confluence-lab-1?project=gitlab-internal-153318) which is currently shut down.
epic