Fetch user's external accounts via user and not site

Created by: artemruts

Description

Fixes #18269 (closed)

Previously errors where thrown when non-admin users tried to access their external accounts through the site GraphQL node, that's not ok. Only admins can access site - that's why we saw errors.
Now users will use correct user node instead.

Tests

With both admin and non-admin users and with non-admin users trying to access other user's external accounts.