[web] Update primaryIdentityPublicKey[s] selector to capture primaryIdentityPublicKeys

Summary:
We update the selector to capture primaryIdentityPublicKeys instead of just the single primary ed25519 key.

We're going to need the {ed25519, curve25519} pair in the login/siwe_auth requests. Going to start with updating the siwe_auth endpoint first since it's simpler/I just spent time working with it.

Depends on D6879

Test Plan: Things continue to work as expected. Will test that login/siwe_auth flows work as expected on web AND native after these changes.

Reviewers: ashoat, tomek, marcin

Reviewed By: ashoat

Differential Revision: https://phab.comm.dev/D6880