It should be possible to generate a retina configuration independent of Helm

Retina configuration is non-trivial, and requires you to remember many different keys and values to create a working configuration. There should exist a subcommand of `retina`, e.g. `retina config generate`, that can generate a working configuration file. Typing only that command (`retina config generate`) should output a completely functional configuration, to the greatest extent possible. Additional flags may be provided to modify the rendered configuration. For example, plugins may be specified with a `--plugins` flag.