[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