osd/osd_types: add min_write_recency_for_promote in pg_pool_t

This field stands for the minimum number of hit sets to check before
promote on write.

Signed-off-by: Zhiqiang Wang <zhiqiang.wang@intel.com>
osd/ReplicatedPG: promote on 2nd write

If min_write_recency_for_promote is
- 0: Promote when there is a write.
- 1: Check if the object is in current hit set. Promote if yes.
- else: Check if the object is in current and other in memory hit sets.
Promote if yes.

Signed-off-by: Zhiqiang Wang <zhiqiang.wang@intel.com>
mon: add osd pool set/get for min_write_recency_for_promote

Signed-off-by: Zhiqiang Wang <zhiqiang.wang@intel.com>