Add a server-side reset() method to end an identified session server-side

[JPustkuchen]

When a user logs out, his identified session should end. This is well implemented in JS: https://posthog.com/docs/product-analytics/identify#reset

Sadly it's not yet available server-side, while it would be a great (and the best) place to do that.
Typically the validated log-out is handled server-side, ending the user session. We should then be able to also reset the session server-side, using the $distinctId parameter.

Something like this:

    /**
     * End the identified session.
     *
     * @param string $distinctId
     * @param bool $resetDeviceId
     * @return bool whether the reset call succeeded
     */
    public function reset(string $distinctId, bool $resetDeviceId)
    {
        return $this->consumer->reset($distinctId, $resetDeviceId);
    }