This is a followup to ROX-28698. While working on that ticket, we noticed that there are two env variables in `pkg/env/sensor.go` that are used to communicate Sensor host address to other services. Those are: 

// AdvertisedEndpoint is used to provide the Sensor with the endpoint it
// should advertise to services that need to contact it, within its own cluster.
AdvertisedEndpoint = RegisterSetting("ROX_ADVERTISED_ENDPOINT", WithDefault("sensor.stackrox.svc:443"),
    StripAnyPrefix("https://", "http://"))

// SensorEndpoint is used to communicate the sensor endpoint to other services in the same cluster.
SensorEndpoint = RegisterSetting("ROX_SENSOR_ENDPOINT", WithDefault("sensor.stackrox.svc:443")) 

There is no need to have two variables that do the same thing - the `StripAnyPrefix` has been added in ROX-28698 to add basic input sanitization to this var. This task is about unifying them - pick one and make sure that it is used correctly.

Extras:

• Those vars exist because we are not always able to reliably determine the namespace in which Sensor is deployed. Find a way to reliably derive the namespace of Sensor, so that we can get rid of both of those env vars.