Add general requirements for PNFD, which mainly cover related TOSCA 

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5.1.10.1. General

Requirement: R-2463

target: PNF

keyword: MUST

introduced: Dublin

The PNF Descriptor (PNFD) provided by PNF vendor MUST comply with TOSCA/YAML based Service template for PNF descriptor specified in ETSI NFV-SOL001.

quirement: R-998862

target: PNF

keyword: MUST

introduced:  Dublin

The PNFD provided by a PNF vendor MUST comply with the following TOSCA Types as specified in ETSI NFV-SOL001 standard :

—tosca.nodes.nfv.PNF

—tosca.nodes.nfv.PnfExtCp

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