ospfd: YANG Model definition for OSPFv2

Initial version of OSPF configuration Yang.

Raised new PR with review comment fixes on top of PR
#6055

Co-authored-by : Santosh P K <sapk@vmware.com>
Co-authored-by : Mobashshera Rasool <mrasool@vmware.com>
Signed-off-by: Mobashshera Rasool <mrasool@vmware.com>

Author: mobash-rasool