[protos] Add initial_device_list field

Summary:
Addresses:

• ENG-7533
• ENG-7868

Added the initial_device_list to registration requests' proto messages.

We need it in the following rpcs:

• RegisterPasswordUserStart
• RegisterReservedPasswordUser
• RegisterWalletUser
• RegisterReservedWalletUser

The WalletAuthRequest is also used in LogInWalletUser so we always put empty string there

Test Plan:
Made sure the change is backwards compatible

1. Compiled native without this changes
2. Applied this change and compiled Identity Service. Added server-side log to print the initial_device_list.is_empty() value.
3. Without recompiling, ran the registration on native.
4. Made sure the value is an empty string
5. Compiled native with changes from this diff, ran registration again and verified it's empty string

Reviewers: ashoat, will

Reviewed By: ashoat, will

Subscribers: tomek, varun

Differential Revision: https://phab.comm.dev/D12017