[Identity] Add DDB table for one-time-keys

Summary:
Add new one-time-keys table for both content and notif keys.

https://linear.app/comm/issue/ENG-4535

Depends on D8642

Test Plan:

cd services/terraform/dev
./run.sh

The two identity-*-onetime-keys should be created.

The constants in service/identity/ are tested later

Reviewers: bartek, varun

Reviewed By: bartek, varun

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D8675