Update specification to add key commitment

Version 2.0 of the various ESDK implementations have added key commitment as another dimension of variability for algorithms suites: https://aws.amazon.com/blogs/security/improved-client-side-encryption-explicit-keyids-and-key-commitment/

At a minimum we need to update the information on the available algorithm suites and especially the fact that the default algorithm suite now depends on your commitment policy: https://github.com/awslabs/aws-encryption-sdk-specification/blob/4b1c0e06435d385fc0593a5619ce686cf2cb79e8/framework/algorithm-suites.md#supported-algorithm-suites

Start with framework/algorithm-suites.md, especially the supported algorithm suites section linked in the issue. Use the AWS key-commitment reference and the issue’s description to identify the information that is missing. Done means the specification documents key commitment, the available algorithm suites, and how the default suite depends on commitment policy.

Written by the indexing model from the issue text.