LU-16087 lprocfs: add histogram to stats counter

LU-16087 lprocfs: add histogram to stats counter

Add histogram to stats counter.
Enable histogram for read/write_bytes in mdt/obdfilter
job stats.

Sample job_stats:
- job_id:          md5sum.0
snapshot_time   : 3143196.864165417 secs.nsecs
start_time      : 3143196.707206168 secs.nsecs
elapsed_time    : 0.156959249 secs.nsecs
  read_bytes:      { samples: 2, ..., hist: { 32K: 1, 1M: 1 } }
  write_bytes:     { samples: 1, ..., hist: { 1K: 1 } }

Lustre-change: https://review.whamcloud.com/48278
Lustre-commit: fde40ce32c91c804cb85be085f2aaf06170047b6

Signed-off-by: Lei Feng <flei@whamcloud.com>
Change-Id: I75b6909c8b63f08b74c3c411ff3dcd27881bb839
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Shuichi Ihara <sihara@ddn.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/49760
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>