ospfd: show ip ospf interface json output format

ospfd: show ip ospf interface json output format

Current json output does not differentiate start of
interface objects. Adding "interfaces" keyword at the
beginning of the interface list. This is useful
when displaying vrf level output along with interface list.

Ticket:CM-19115
Testing Done:
show ip ospf vrf all interface json
show ip ospf vrf all interface <specific intf> json
show ip ospf interface json
show ip ospf interface <specific intf> json

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