dataspace protocol: Add missing notify methods on TransferProcess services

[ndr-brt]

Feature Request

Add methods on TransferProcessService that will permit the (currently called) message handlers to being able to apply the needed state transition.

e.g. currently in TransferProcessService there's the notifyStarted method, that will be called when a TransferStartMessage is received from a provider, and the referred TransferProcess state need to be changed accordingly.

Adding the notify prefix will help to distinguish methods where actually an action is performed on the connector to the ones that represent an action taken on the counter-part and to keep the present tense (typical for an action/command).
e.g. terminate/notifyTerminated .

Which Areas Would Be Affected?

transfer process

Why Is the Feature Desired?

cleanup