Add hs ls command to get asset listing

[TheWebTech]

To enable developers to work more and more locally without relying on the design manager as much, it would be nice to have an ls like command.

hypothetical command:

hs ls <path> --portal=<portalId>

path is optional, if left blank returns root directory.

When executed returns a list of files and folders in the specified directory.

Use cases:

• Developers can identify the folder names/paths that they want to fetch/upload to easier without relying on the Design Manager UI.

• Could also be used as a safe "testing" mechanism to ensure a hubspot.config.yml file is properly configured. (see Slack)

caveat there is no concept of hs cd and that may be requested after. A cd command could be confusing to work with.

[miketalley]

I think the best way to go about this would be to add a GET for /folders/by-path/{fullPath} that returns the folder and then if we have a match we can GET /folders/contents using that folder.id and list the folders and files from the response.