fix convert_imgs to use correct worker sizxe

[kathleenleeper]

Re: converting ims images that are larger (or have more files), fixing the memory error that occurs. Hacky fix: in nextflow.config, changing line 116 to

            withLabel: 'memory_medium' {
                queue = 'cpu-r5-2xlarge'
                memory = '60 GB'
                cpus = 8
            }