[identity] Save initial device list to DDB

Summary:
Final server-side part for initial device list. If it is present, a new register_primary_device() is called, which is very similiar to existing add_device() but stores the received device list instead of generating a new one. Also, it requires previous device list to be empty and doesn't perform the reoredering.

Depends on D12090

Test Plan:
After each of below actions, called GetDeviceListHistoryForUser RPC:

• Registered password user without initial device list - the list was generated by Idenitity (previous behavior)
• Registered password user with initial device list - the list was stored along with signature
• Registered wallet user with initial device list - the list was stored along with signature

The RPC failed:

• Sent initial device list that was invalid JSON
• Without signature
• With invalid signature
• With more than 1 device
• With device ID not being the ed25519 from device key upload
• With lastPrimarySignature being present

Reviewers: kamil, will, varun

Reviewed By: kamil, varun

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D12091