Choosing identity dynamically to call transactions

[mikaellafs]

• Enable choosing which identity to use when calling transactions via ccapi:
  Add a header User specifying which certificate to use: Admin or User1 availables.
• Update tx callers format in chaincode
• It uses cc-tools from branch feature/permissioning. For test, please uncomment this (ensure cc-tools repository path and it is in the correct branch):

// chaincode/go.mod
replace github.com/goledgerdev/cc-tools => ../../cc-tools