feat: add n and threads

tasks/DownSample.wdl

 
   String sample_id
   File fastq
-  Float p
+  Float? p
+  Int? n
   String docker
   String cluster_config
   String disk_size
-  
+
   command <<<
     set -o pipefail
     set -e
-    seqkit sample --two-pass -s 100 -p ${p} ${fastq} -o ${sample_id}.fastq.gz
+    nt=$(nproc)
+    if [ ${p} ]; then
+      seqkit sample --two-pass --threads ${nt} -s 100 -p ${p} ${fastq} -o ${sample_id}.fastq.gz
+    else
+      seqkit sample --two-pass --threads ${nt} -s 100 -n ${n} ${fastq} -o ${sample_id}.fastq.gz
+    fi
   >>>
 
   runtime {

workflow.wdl

   
   String sample_id
   File fastq
-  Float p
+  Float? p
+  Int? n
   String docker
   String cluster_config
   String disk_size
       sample_id=sample_id,
       fastq=fastq,
       p=p,
+      n=n,
       docker=docker,
       cluster_config=cluster_config,
       disk_size=disk_size