[services-lib] Implement DDB Attr conversions, deprecate old methods
Summary:
Implements traits introduced in the previous diffs for basic types and marks legacy methods as deprecated.
Depends on D8789
Test Plan: Tested later in the stack
Reviewers: michal, jon, varun
Reviewed By: michal
Subscribers: ashoat, tomek
Differential Revision: https://phab.comm.dev/D8790