[identity][terraform] Create DDB index for deviceID

Summary:
Addresses ENG-8382.
Introduced index to find devices only by deviceID.

Test Plan:
terraform, localstack,

awslocal dynamodb scan --table-name identity-devices --index-name deviceID-index

returns userID, deviceID and loginTime attributes

Reviewers: varun, will, marcin

Reviewed By: varun

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D12348