Added json schema and modified checks on MethodNotImplemented

...VNFPackageManagement-API_nxw/IndividualSubscription.robot

...3/VNFPackageManagement-API_nxw/IndividualVNFPackage.robot

...ckageManagement-API_nxw/SOL003-VNFPackageManagement.robot

SOL003/VNFPackageManagement-API_nxw/Subscriptions.robot

...ackageManagement-API_nxw/VNFDInIndividualVNFPackage.robot

...03/VNFPackageManagement-API_nxw/VNFPackageArtifacts.robot

SOL003/VNFPackageManagement-API_nxw/VNFPackageContent.robot

SOL003/VNFPackageManagement-API_nxw/VNFPackages.robot

...geManagement-API_nxw/schemas/PkgmSubscription.schema.json

...kageManagement-API_nxw/schemas/ProblemDetails.schema.json

...anagement-API_nxw/schemas/additionalArtifacts.schema.json

...03/VNFPackageManagement-API_nxw/schemas/links.schema.json

...ckageManagement-API_nxw/schemas/softwareImage.schema.json

...FPackageManagement-API_nxw/schemas/vnfPkgInfo.schema.json