ospfd: show ip ospf neighbor json output format

ospfd: show ip ospf neighbor json output format

Current json output does not differentiate start of
neighbor ip object. Adding "neighbors" keyword at the
beginning of neighbor list. This is useful when
displaying vrf level output along with neighbors
list.

Ticket:CM-19097
Testing Done:
show ip ospf neighbor json
show ip ospf vrf all neighbor json

Signed-off-by: Chirag Shah <chirag@cumulusnetworks.com>