Add a databroker method to load a catalog from a intake catalog file (v2 config file)

[gwbischof]

Currently the recommended way to create a v2 databroker catalog is intake.open_catalog(catalog_file)

I think we should add a databroker method to load v2 config files, so that users don't need to know about intake.

Thoughts about how this should be implemented?

Some ideas to start the conversation:

• update databroker.v1.from_config() so that it can also load v2 catalogs. Should this method parse the config_file to determine if it is a v1 or a v2 catalog? Or should it get an argument to specify the type of catalog?
• make a databroker.v2.from_config() that is an alias for intake.open_catalog()