Align subscription functionality with the retrieve API

[akoshunyadi]

Problem description
Copied from camaraproject/DeviceStatus#248

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

[sachinvodafone]

It seems, @bigludo7 responded on previous repository as :

Yes make sense to align.

Following your proposal it will reflect as such for event-type value:

org.camaraproject.device-reachability-status-subscriptions.v0.reachability-connected (new) - Event triggered when a disconnected device turns connected.

org.camaraproject.device-reachability-status-subscriptions.v0.reachability-disconnected (existing) - we keep existing definition: Event triggered when the device is not connected.

org.camaraproject.device-reachability-status-subscriptions.v0.reachability-data (existing) - we keep existing definition: Event triggered when the device is connected to the network for Data usage (regardless of the SMS reachability).

org.camaraproject.device-reachability-status-subscriptions.v0.reachability-sms - we keep exisisting defintion: Event triggered when the device is connected to the network only for SMS usage

And of course we keep org.camaraproject.device-reachability-status-subscriptions.v0.subscription-ends

and understanding looks fine to me too.