Ledger Enclave Strategy

The integration of the Ledger Enclave is one of the fundamental pillars in the FPC security architecture, however, the implementation is also challenging.

This issues continues the discussion based on the [FPC RFC](https://github.com/hyperledger/fabric-rfcs/pull/21).

- [ ] Define minimal set of functionality implemented by Ledger Enclave (and which other features we can safely ignore and which one we will have to detect but abort)
- [ ] Develop short-/mid-/long-term working plan for development.
- [ ] define process on how to guarantee initial consistency and main invariant as fabric evolves (e.g., via code cross-referencing, potentially indirect via a HL fabric validation flow pseudo-code which abstract but also identifies location of fabric code) and potential some scripts which help identify crucial changes in validation logic when upgrading fabric versions)