[API]: Unify Send API

[harlem88]

Currently each Astarte Device SDKs has a different name for the function that allows publishing data to an Astarte instance.

We want to unify the Send API across all SDKs to avoid confusion for the end user, who may use different SDKs for various use cases and could become disoriented.

All SDKs will implement the unified API for publishing data to an Astarte instance.

API for publishing a property value :

def set_property(...);

def unset_property(...);

API for publishing a individual value :

def send_individual(...);

API for publishing a object value :

def send_object(...);