[identity] Get device PlatformDetails from metadata

Summary:
Passed metadata PlatformDetails all the way through to DDB storage in all login/registration actions (where DeviceKeyUpload is present)
Added parsing and verification for device type.

Depends on D12270

Test Plan:
Combined test plans from D12269 and D12270:

• Modified client to have additional metadata args
• Called LogInUser to verify that they're stored in DDB
• Deliberately malfolmed client device_type to make sure DeviceKeyUpload value is preferred and a warning is displayed

Reviewers: varun, marcin, will

Reviewed By: marcin

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D12271