ReplicatedPG: handle FLAG_OMAP on promote and copyfrom

Fixes: #7967
Signed-off-by: Samuel Just <sam.just@inktank.com>
osd/: track num_objects_omap in pg stats

Fixes: #7831
Signed-off-by: Samuel Just <sam.just@inktank.com>
ReplicatedPG::agent_choose_mode: exclude omap objects for ec base pool

Fixes: #7831
Signed-off-by: Samuel Just <sam.just@inktank.com>