Consider S3 properties on API Gateway StaticRoute

[joeduffy]

The way Static Routes for API Gateway work today is convenient when I want to provision and upload S3 buckets/objects as part of the program defining the API Gateway itself. It's possible, however, that I either want to use an existing set of S3 resources, or that I'd like to provision them manually so that I can control specific properties of the S3 resources.

It would be nice if we had bucket and bucketObject properties on the StaticRoute type that would let me pass these instead of path, if I prefer using that style. This is similar to how we do the EventHandlerRoute, which can accept an inline callback if I want, but where I can always drop back to passing a Lambda object explicitly if that's what I prefer.