feat(auth): Enable resumable SignIn

[joon-won]

Description of changes

• Enable v6 users to have an option to continue SignIn process after a full browser reload by storing, then utilizing session in session storage

Issue #, if available

• Ability to resume authentication flow #10469
• Ability to resume authentication flow (v6) #12810

Description of how you validated changes

• Unit tests (IP)
• Smoke Test on sample application

Checklist

• PR description included
• yarn test passes
• Tests are changed or added
• Relevant documentation is changed or added (and PR referenced)

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[israx]

Thanks @joon-won . We are getting close. A couple of things,

1. we should consider creating an internal sync sessionStorage util so we don't have to change the sync behavior of the signInStore

2. we must avoid modifying state at all costs. Left comments bellow and pointed out the tests needed