[keyserver] double-write to identity service from siweAuthResponder callpoint

Summary:
we should double-write siwe account creations and logins to the identity service using the loginUserWallet function in the rust-node-addon.

Depends on D6945

Test Plan: logged in on web with my rainbow wallet, saw that the same user data was written to MariaDB and DynamoDB

Reviewers: ashoat, jon, bartek, atul

Reviewed By: ashoat

Subscribers: tomek, atul

Differential Revision: https://phab.comm.dev/D6946