Upstream SGX Async I/O

[MoSalemIb]

Calling userspace from an SGX enclave is very slow. It’s much faster to copy data out of the enclave and let it be picked up (asynchronously) by a userspace thread. Similarly the response can be returned by placing it in a return queue in userspace. That avoids that the enclave needs to be exited. Mohzen has worked on this and we use it in production. Most of the code however is in a feature branch. Yuxiang recently also took a look at this, and I started reviewing his updated branch, but this work has been paused for now until the mbedtls work is completed.

[BelalH]

PR: #404

[raoulstrackx]

PR: #404

There's another PR based on that one: #441

[BelalH]

1. finish the PR review
2. create new tickets (improvements we found during the review)
3. test new async io internally
   a. test before new crate
   b. test after the new crate
4. RELEASE