attach abstract method
Called once by Digia.register(). Store the host and start listening
to the CEP SDK.
Core never holds a trigger: a delivery made before the SDK is ready
settles at once as dropped (not_initialized, not_ready or
initialization_failed). The plugin holds early payloads in its own
PendingPayloadBuffer while DigiaCEPHost.isReady is false. Attached
after a failed init, it learns of it from a delivery that drops
initialization_failed.
Implementation
void attach(DigiaCEPHost host);