[identity] bump aws-config and aws-sdk-dynamodb crate versions

Summary: these were pretty outdated. tested a couple client calls to DDB to make sure nothing broke

Test Plan: called the generate nonce and get user ID RPCs and the DDB client was able to read from/write to test tables

Reviewers: jon, bartek

Reviewed By: bartek

Subscribers: ashoat, tomek, atul

Differential Revision: https://phab.comm.dev/D7256