Proposal: Supporting basic remote caching option at Scipio's `prepare` command

[Subeen Park]

Hi there! I've been actively using your project, and I must say it's been incredibly helpful. However, I've noticed that I need to create an additional package solely for storing cache on a remote storage. It would be great if Scipio's caching configuration could include a basic storage option.

Here's what I envision for the feature:

scipio prepare --cache-policy storage

When the cache policy option is set to storage, Scipio will automatically search for a StorageConfig.json file in the same location as the Package.swift file. It will then proceed to set up remote cache storage using scipio-s3-storage from #66. An example of the StorageConfig.json file would look like this:

{
	"endpoint": "http://127.0.0.1:9000",
	"accessKey": "SOME_ACCESS_KEY",
	"secretKey": "SOME_SECRET_KEY",
	"bucketName": "SOME_BUCKET_NAME",
	"actorKind": ["producer", "consumer"]
}

I would like to hear your comments on this idea. If you find it reasonable I’ll try to come up with a PR.