Use minio instead of s3

[zzl221000]

Our environment only has a local network, minio cluster, and right now arroyo does not support configuring the endpoint parameter of s3.
Normally, s3-compatible object stores should all work.

[mwylde]

Hey @zzl221000 this is now supported in master, and will be part of release 0.6 next week. Object store paths are now specified as a full URL, which can include other endpoints. See #296 for the details.