Add a field to preflight response specifying if the resource cannot be accessed

[andmor-]

If the switchboard cannot access a resource, this could be communicated and in that case the calling application could disable the option in the dropdown.

One idea is to add the field reachable=[true|false] to the response.

Ref: https://clarineric.slack.com/archives/GCX9NPRTM/p1671634737616829