extract optional and required SGX claims provided by Open Enclave

[THS-on]

This change implements the extraction of all the optional and required SGX claims provided by Open Enclave.
The main motivation was to get the UEID which matches the QEID, so that it is possible to tie the quote and machine where the enclave is running on together. The additional information gives more flexibility to attest the system.

Changes around the Report struct:

• Added UEID field which is QEID for SGX
• Added SGXClaims field which holds the optional and required claims
• Added conversion functions between internal and attestation structs. What is the reason behind the duplication of those structs?

Two new structs SGXOptional and SGXRequired are introduced to hold the respective claims.

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[CLAassistant]

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[thomasten]

Thank you for wanting to contribute to EGo! The feature makes sense and we would like to accept it. I haven't reviewed the implementation in detail yet. You need to sign the CLA (see above) so that we can accept your contribution.

[THS-on]

I need to check, if I can sign the CLA. This might take longer time. Is it possible to contribute changes without the CLA?

[thomasten]

No, unfortunately not.