Update catalog content retrieval method

[everettraven]

Upon completion of https://github.com/operator-framework/catalogd/milestone/4 catalogd will have a new method for serving catalog content via a HTTP server as opposed to Kubernetes CustomResources. Once the milestone is complete and a release of catalogd containing the changes has been cut, this method for retrieving catalog content for resolution needs to be updated.

[joelanford]

This is currently planned in catalogd v0.6.0. See operator-framework/catalogd#139