Merge "AttestationKey documentation" am: c46f9da49f am: 5df02652c1 am: 237ecec162 am: ff9fce151e

Original change: https://android-review.googlesource.com/c/platform/hardware/interfaces/+/1674665

Change-Id: I1707ef6d258f66d9055e271e95687782e8eed9c8