support alternative S3 compatible storage backend

[C-Sto]

For environments where different object storage is used but is s3 compatible (eg, DigitalOcean Spaces, MinIO etc) it would be good to be able to supply the endpoint. As far as I can tell, this would require modifying the StorageOptions struct to contain the relevant inputs to the endpoint resolver (partition ID, URL, region)

private-armory/api/storage/s3.go

Line 207 in 79b84b2

s3Config, err := config.LoadDefaultConfig(context.TODO())

see https://stackoverflow.com/questions/67575681/is-aws-go-sdk-v2-integrated-with-local-minio-server for example