rgw/sync-policy: Support disabling per-bucket replication

rgw/sync-policy: Support disabling per-bucket replication

When the zones replicate, allow disabling replication
for specific buckets using sync policy.

These are the semantics to be followed while resolving the policy
conflicts -

==================================================
zonegroup		bucket		Result
==================================================
enabled			enabled		enabled
			allowed		enabled
			forbidden	disabled
allowed			enabled		enabled
			allowed		disabled
			forbidden	disabled
forbidden		enabled		disabled
			allowed		disabled
			forbidden	disabled

In case multiple group policies are set to reflect for any sync pair
(<source-zone,source-bucket>, <dest-zone,dest-bucket>), the following
rules are applied in the order -
1) Even if one policy status is FORBIDDEN, the sync will be disabled
2) Atleast one policy should be ENABLED for the sync to be allowed.

Various cases tested are outlined here -
https://docs.google.com/document/d/19oBQA-bYxLBR4BnekA2DTwJJaTFvjAfrqAk9G3RGU0I/edit#heading=h.4qac9dpc76m

Signed-off-by: Soumya Koduri <skoduri@redhat.com>