Improve authentication mechanism for device-reachability-status-subscription

[bigludo7]

Problem description
Accordingly to Commonalities decision in camaraproject/Commonalities#580 and camaraproject/Commonalities#583 we have to introduce Private JWT key in the device-reachability-status-subscription model

Expected behavior

Alternative solution

Additional context

[eric-murray]

Fixed following use of common CAMARA schemas