crimson/os/seastore: implement disk and writer level stats reporting

crimson/os/seastore: implement disk and writer level stats reporting

At SeaStore level, to understand the device balances:
* IOPS
* per-writer depth
* bandwidth
* IO size

Picking a particular SeaStore shard, to understand:
* Per device tier write status
* Per writer status in a device tier
* Per transaction type status
* How each type of transactions write through the writers

Signed-off-by: Yingxin Cheng <yingxin.cheng@intel.com>
(cherry picked from commit 8f67346015f0917cf56f0534fc316af8560921de)