send posthog event when auth info changes

[shalom938]

the plugin send GLOBAL/SET_USER_INFO with user id to the ui whenever auth info changes, the user id is the user id returned from the backend on login and refresh.
it will help debugging if UI will send posthog event whenever the user id changes.
NOT on every message because there may be many messages sent with the same user id, only when user id changes,
from null to nonnull
from nonull to null
and a different user id