Sealed Storage for ECC

**Description**

To allow ecc restarts (e.g., due to peer restart, #282, or just ecc external builder getting terminated by peer and restarted), ecc will eventually require to store enclave and cc secrets to sealed storage.

- [ ] API definition
- presumably we can do that as only local library calls with all ecalls/ocalls behind the scenes?
- [ ] implementation of API as libraries
- will need a trusted and an untrusted component, although likely only one of them will have public interfaces which are called from other call, the other side just implements ecalls/ocalls called from the "other" side of the library ...
- [ ] Integrate library into ECC

**Link to feature or bug**

**Link to dependent issues**

No files, tests, or entry points are named. Start by reading the ECC context and dependent issue #282, then resolve the API and trusted/untrusted library design described in the checklist. Done means the API is defined, both library components are implemented, and the library is integrated into ECC.

Scritto dal modello di indicizzazione a partire dal testo della issue.