LU-16228 utils: add lljobstat util

LU-16228 utils: add lljobstat util

lljobstat util read datas from job_stats file(s),
parse, aggregate the data and list top jobs.

For example:
$ ./lljobstats -n 1 -c 3
---
timestamp: 1665984678
top_jobs:
- ll_sa_3508505.0: {ops: 64, ga: 64}
- touch.500:       {ops: 6, op: 1, cl: 1, mn: 1, ga: 1, sa: 2}
- bash.0:          {ops: 3, ga: 3}
...

Signed-off-by: Lei Feng <flei@whamcloud.com>
Test-Parameters: trivial
Change-Id: I0c4ac619496c184a5aebbaf8674f5090ab722d72
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/48888
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>