support EC2 instance attestation

**What I'd like:**
I'd like to have a way to configure AWS variants to support [EC2 instance attestation](https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/nitrotpm-attestation.html), with the end goal of being able to configure EC2 instances via user-data and arriving at a reasonable remote attestation story.

The ideal end state is to be able to assert that a particular system can only run trusted container images using trusted OCI runtime specs, and furthermore that it's not possible to change that configuration afterwards without changing the reported PCR values, bricking the machine, or both.

**Any alternatives you've considered:**
The existing AMIs can be re-registered with a TPM2 device, and some of the PCR values are already populated in a useful way (7 and 14).

However, making this a first-class feature with documented behavior for PCR measurements and OS-level guarantees is required to reach the ideal end state.