Enable support for Fabric Private Chaincode

[mbrandenburger]

Is your feature request related to a problem? Please describe. Fabric Private Chaincode is a new type of Fabric Chaincode which allows to execute smart contracts with the help of trusted execution environments (i.e., Intel SGX) to enhance protection of a smart contract and data.

Fabric Private Chaincode requires the use of external builders / chaincode-as-a-service feature in Fabric. Adding support for this may required to resolve issue #1284 first.

[sownak]

External chaincode support has been added as per #2293 The Private chaincode or private data collection can be tested now.

[suvajit-sarkar]

Stale issue, closing it