Location of idkey in plugin-configuration for overriding meta.id as default for matching samples

[sgsutcliffe]

When the meta.id key needs to be replaced for matching samples the configuration file needs to be formatted in the files key
e.g.,

iridanext {
    enabled = true
    output {
        path = "${params.outdir}/iridanext.output.json.gz"
        overwrite = true
        files {
            idkey = "irida_id"
            global = ["**/summary/summary.txt.gz"]
            samples = ["**/assembly/*.assembly.fa.gz"]
        }
        metadata {
            samples {
                csv {
                    path = "**/output.csv"
                    idcol = "column1"
                }
  }
    }
}

This location makes sense if it is being used to identify files but it can also be used to identify metadata, so it might be more intuitive to allow the idkey in the output { } and/or in the metadata { } .