Add configuration option(s) for instructing the S3 API to not upload files to iRODS

[korydraughn]

Enhancement / Performance

Disabling uploads to the iRODS server would allow us to measure the upload speed from clients to the S3 API.

Storing the uploaded data locally would be optional as well.

For example, the config file could grow two new options:

{
    // Controls whether data is uploaded to iRODS.
    // Defaults to true. When set to false, data is
    // NOT uploaded to iRODS.
    "upload_data_to_irods": true,

    // Controls whether intermediate data (e.g. part files, etc)
    // is stored in a local directory. This only applies
    // when "upload_data_to_irods" is false.
    "store_intermediate_data": true,

    // The directory where intermediate data is stored.
    // This only applies when "store_intermediate_data"
    // is true.
    "intermediate_data_directory": "/tmp/irods_s3_api"
}

We'd need to think about how the intermediate_data_directory property would play with the multipart_upload_part_files_directory property.