Generalize metadata schemas for wawaka common contracts

[marcelamelara]

Currently, the contract code metadata focuses on validating the code hash on the ledger. However, it would be useful to include more general metadata about contracts such as contract type (wasm vs native), or CDI-type metadata.

This issue may also be related to #294 .

[cmickeyb]

Contract metadata schema is currently defined as:
{ "verifying_key" : "", "encryption_key" : "" }

Contract code metadata schema is currently defined as:
{ "code_nonce" : "" }

These reflect the information that is necessary to verify attestations generated by the ledger as to the identity of a contract object (and to bind an encryption key to that object).

[cmickeyb]

@marcelamelara do you have a more specific request? i would expect any application/contract that wants to use the additional data to extend this function. It would be rather constraining to force all applications to use the additional metadata.

[cmickeyb]

And I think this issue is completely independent of #294. One occurs in the enclave and is part of the fundamental trust relationship between the contract, the ledger and the user. This code is about establishing run-time trust between two separate contracts.