Clair v4 goroutine leak when requesting POST index_report

I noticed during some metrics work that the number of goroutines was increasing, this lined up with the number of requests made to `POST /index_report`. 

It looks like it is coming from the `pgxpool.ConnectConfig()`, specifically from `claircore/libindex/controllerfactory.go:controllerFactory`.

Acceptance:

• Goroutines should stay stable after requests to `POST index_report`