osd/scrub: extract scrub backend code into separate classes

osd/scrub: extract scrub backend code into separate classes

A refactoring of the scrub backend code (all Scrub related code
that checks/manipulates objects' (meta)data).

Part of the refactoring was breaking long chunks of code into
separate functions. In order to avoid passing endless lists
of state parameters from/to these new methods, the scrub backend
state is now maintained within its own objects.

a change to note:
Instead of two scrub-map collections - one that holds all
incoming maps, and one that holds pointers to all of those incoming
plus the one we (the Primary) manage - just use one collection
for both incoming and our own.

Signed-off-by: Ronen Friedman <rfriedma@redhat.com>
Split from "osd/scrub: minor fixes split from main "scrub backend" commit"

Split from "osd/scrub: scrub components embedded documentation"

fix

Signed-off-by: Ronen Friedman <rfriedma@redhat.com>
osd/scrub: fix the scrubber backend to include all PR #42735

Signed-off-by: Ronen Friedman <rfriedma@redhat.com>