script: add dcache pool benchmark command

[kofemann]

Motivation:
Often admins want to know the expected I/O rates that a pool can provide. The desired benchmarks can be hart to configure. This, it makes sense to provide a 'good starting point' with dcache.

Modification:
update dcache command to provide pool benchmark command that will benchmark all configure pools in the layout file that that host. Optionally, a specific directory can be used.

Result:
simple test to benchmark pools filesystem

$ dcache pool benchmark

  Running fio benchmark for pool pool_write@dCacheDomain.

seqwrite: (g=0): rw=write, bs=(R) 4096B-4096B, (W) 4096B-4096B, (T) 4096B-4096B, ioengine=libaio, iodepth=1
seqread: (g=1): rw=read, bs=(R) 4096B-4096B, (W) 4096B-4096B, (T) 4096B-4096B, ioengine=libaio, iodepth=1
randread: (g=2): rw=randread, bs=(R) 4096B-4096B, (W) 4096B-4096B, (T) 4096B-4096B, ioengine=libaio, iodepth=1
concurrent_write: (g=3): rw=write, bs=(R) 4096B-4096B, (W) 4096B-4096B, (T) 4096B-4096B, ioengine=libaio, iodepth=1
...
concurrent_randread: (g=4): rw=read, bs=(R) 4096B-4096B, (W) 4096B-4096B, (T) 4096B-4096B, ioengine=libaio, iodepth=1
...
fio-3.40
Starting 48 threads and 3 processes
Jobs: 1 (f=1): [_(36),V(1),_(14)][100.0%][r=556MiB/s][r=142k IOPS][eta 00m:00s]
seqwrite: (groupid=0, jobs=1): err= 0: pid=156310: Fri Mar  6 11:57:47 2026

....

Run status group 0 (all jobs):
  WRITE: bw=636MiB/s (667MB/s), 636MiB/s-636MiB/s (667MB/s-667MB/s), io=10.0GiB (10.7GB), run=16110-16110msec

Run status group 1 (all jobs):
   READ: bw=628MiB/s (659MB/s), 628MiB/s-628MiB/s (659MB/s-659MB/s), io=10.0GiB (10.7GB), run=16298-16298msec

Run status group 2 (all jobs):
   READ: bw=41.0MiB/s (43.0MB/s), 41.0MiB/s-41.0MiB/s (43.0MB/s-43.0MB/s), io=10.0GiB (10.7GB), run=249909-249909msec

Run status group 3 (all jobs):
  WRITE: bw=1738MiB/s (1822MB/s), 1738MiB/s-1738MiB/s (1822MB/s-1822MB/s), io=240GiB (258GB), run=141418-141418msec

Run status group 4 (all jobs):
   READ: bw=1845MiB/s (1935MB/s), 1845MiB/s-1845MiB/s (1935MB/s-1935MB/s), io=240GiB (258GB), run=133205-133205msec

Acked-by: Marina Sahakyan
Target: master
Require-book: no
Require-notes: yes
(cherry picked from commit 2e61583)