Consider exposing tee_qv_free_collateral as a rust API

[nick-mobilecoin]

tee_qv_free_collateral will communicate with the system quote provider to get collateral.
There is a default implementation available that uses a PCCS to get a cached version of the quote collateral data.

Using tee_qv_free_collateral may be a more consistent way to get the collateral.
Otherwise the enclave host will need to ping

• TCB https endpoint

• QE identity https endpoint

• CRL endpoint
  to get all of the collateral.

• Add trait to get verification collateral #341

• Add mc-sgx-dcap-types::Collateral #342

  • Remove the CollateralPointer added in Add trait to get verification collateral #341, this was a temporary holder to better understand the internals of sgx_ql_qve_collateral_t.