Implement real storage backend

[calvinmclean]

Implement another storage.Client that uses actual database backend, whether it is SQL or NoSQL.

I recently found madflojo/hord and added support for local file storage in this PR. Now, I can switch my local storage solution to use this and will just need some additional configuration to support multiple KV and NoSQL storage solutions.

Requirements

• Implement storage.Client with type KV that can be compatible with all current hord backends
• hord will return an error if something is not found. I need to either handle this to just return nil, nil like other clients or implement a new NotFound error that can be used by all client implementations

Open Questions

• What happens to my combined configmap/yaml storage? YAML storage will be replaced by hord, but it won't support saving to a configmap. I could just remove that since I don't use it anymore, but it is also fine to keep it around
• Currently, everything relies on Zones being managed as a map under a Zone, but this doesn't work as well with a KV store. The options are requiring editing Zones by reading/writing an entire Garden, or storing Zones separately and having the Garden ID in the Key so it can be found by Garden ID

[calvinmclean]

It’s probably best to wait until after implementing #22 since that will be a major storage refactor