Merge pull request #44591 from athanatos/sjust/wip-seastore-flush

crimson/os/seastore: avoid empty Transactions by adding explicit flush() call

Reviewed-by: Yingxin Cheng <yingxin.cheng@intel.com>

diff --cc src/crimson/os/seastore/journal.cc
Simple merge

diff --cc src/crimson/os/seastore/journal.h
Simple merge

diff --cc src/crimson/osd/pg.cc
Simple merge