added doc for SOL005 notifications

SOL005/NSDManagement-API/NSDManagementNotification.robot

SOL005/NSDManagement-API/environment/variables.txt

...API/schemas/PnfdOnboardingFailureNotification.schema.json

...gement-API/schemas/PnfdOnboardingNotification.schema.json

SOL005/NSPerformanceManagement-API/Notifications.robot

...NSPerformanceManagement-API/environment/notifications.txt

SOL005/VNFPackageManagement-API/Notifications.robot

SOL005/VNFPackageManagement-API/environment/variables.txt

...ment-API/schemas/VnfPackageChangeNotification.schema.json

...-API/schemas/VnfPackageOnboardingNotification.schema.json