[web] use identity service to set SIWE nonce in siwe-login-form

Summary:
if usingCommServicesAccessToken, we should get the nonce from the identity service and set the state variable to that value

Depends on D11018

Test Plan: verified that the action was successful in redux, console logged the state variable to confirm it was set

Reviewers: ashoat, inka, tomek

Reviewed By: ashoat

Differential Revision: https://phab.comm.dev/D11019