[device-reachability-status-subscriptions] Align functionality with the retrieve API

[akoshunyadi]

Problem description
device-reachability-status supports a differentiated reachability information like, "only data, "only sms", "data and sms" or just "reachable"
device-reachability-status-subscriptions remained on the old stand where data covers "data only" or "data and SMS", and SMS connectivity means "SMS only"

Possible evolution
Align the subscription API with the retrieve API and provide similar event types. To be discussed if we can support multiple event types for a subscription.

Possible solution, subscription even types (connected-data and connected-sms can be combined):

• disconnected (none)
• connected (data or sms)
• connected-data (data is connected regardless of sms)
• connected-sms (sms is connected regardless of data)

Alternative solution

Additional context