Overview for projects with enabled specific service

Dev: https://dev.gitlab.org/gitlab/gitlabhq/issues/2148

During call, a customer raised an issue that they do not know how many of their projects have a specific service enabled.

They find this very hard to administer as different projects have different services enabled. They would like to see some sort of overview in the admin section of service templates for each project that uses that service.

I already set the customer expectations for this by saying that it wouldn't be efficient and would be hard to incorporate in the UI.

It makes sense to me why an admin would need this so I am wondering if there is a way to do this, maybe with a filter on /admin/projects ?

cc/ @dzaporozhets @marin @patricio

Proposal (updated 2020.05.29)

Much has changed since 2015, when this issue was first created. Instead of improving Service Templates, we are in the process of bringing project level integrations to the instance and group levels. We are referring to this update as mass-integrations (see parent epic). Therefore it makes sense to add this desired functionality to the new instance and group levels integrations.

JTBD framing:

When, setting up or making changes to a mass-integration, I want to be able to see which projects already use a specific integration. So I can better manage all integrations across the organization, avoiding disruptions and making it clear which projects will be affected by my changes.

Summary of updates

1. Integrations list (for instance and group levels): Add new column with a count of all the active projects using each integration
2. Link the count number to a new tab view called "Active integrations" found under the integration's detail view
3. Allow for the table to be sortable
4. In the "All projects using {integration-name}" table, include a column called: "Using custom settings" which will help the admin understand with projects are overriding their configuration settings. This should then link to the the "Projects overriding these settings tab.

Once implemented, this table will lay the groundwork for being to surface which projects are using custom settings. #218252[integration-active-integrations-table-custom-settings.png]

See latest mockups in the Designs section below.