Add upload-assets-to-s3 task

This adds a new task which can be used to upload a directory of files to an S3 bucket setting the correct mime and encoding types and cache control.

Usage: n-heroku-tools upload-assets-to-s3 [options]

Uploads a folder of assets to an S3 bucket

Options:
  --accessKeyId <accessKeyId>          AWS access key ID
  --secretAccessKey <secretAccessKey>  AWS secret access key
  --directory <directory>              Directory containing the assets to upload (default: "public")
  --bucket <bucket>                    Name of the S3 bucket to upload into (default: "ft-next-hashed-assets-prod")
  --destination <directory>            Name of the destination directory to upload into (default: "hashed-assets/uploaded")
  --extensions <extensions>            A comma delimited list of file extensions to find and upload (default: "js,css,map,gz,br")
  --cache-control <seconds>            Optionally specify a cache control value (default: "public, max-age=31536000, stale-while-revalidate=60, stale-if-error=3600")