[attestation client] Bind the disk decryption value to the TPM using a TPM2_policypassword

[nbouchinet-anssi]

At the end of the enrollment, while using the --pcr-extend option, a random generated blob is extended to PCR9, this blob can later be used for a TPM2_policyPCR LUKS2 encryption key sealing using systemd-cryptenroll for example. It is then stored on server side and returned upon attestation success.

This blob should be sealed to the TPM using a TPM2_policypassword before sending it for storage at server side, thus, disk decryption will be restricted to a password known by the user.