Add 'published' boolean property to Place entities

[akamicah]

(Imported from overte-org/overte-metaverse#1 by AleziaKurdis)

We must be able to use a placename without have this place name published in the explore app.
to be able to use hifiurl, to move between domain, we need at least a placename, but we might not used this placename for advertising. It can be purely for the addressing functionality. (there is not too much other alternative outside IP:port)

Some people want to have a navigability without be listed.

To address this, we would need to:
1- Add a property "published" to the "place" entity. (boolean)
2- Add a checkbox in the Place editor in the metaverse dashboard.
3- Exclude the places where the property "published" would be set to true, from this specific api: GET /api/v1/places (only this one, not any other)