add fleetctl convert --gitops functionality

[dherder]

Problem

As a Fleet admin, it is not clear why I need a different format of .yml for use with gitops. I have already configured my fleet server and don't want to start from scratch with gitops, but I want to use what I have already defined in Fleet to build out my gitops strategy. This means that I need to "get" all config from Fleet with a fleetctl get command and the convert config files to a format that gitops uses.

Potential solutions

have some kind of fleetctl convert --gitops option that converts regular fleet .yml documents into gitops friendly documents.