Make receiver data delivery guarantees explicit (#4262)

Resolves #4261

We want to make this explicit and ensure all receivers follow this pattern.
It is important for applications of the Collector where it is delivery guarantees are critical.

The OTLP receiver correctly follows the guarantees. Other receivers may need to be audited
to ensure compliance.

Author: tigrannajaryan

component/receiver.go

@@ -22,6 +22,15 @@ import (
 )
 
 // Receiver allows the collector to receive metrics, traces and logs.
+//
+// The receivers that receive data via a protocol that support acknowledgements
+// MUST follow this order of operations:
+// - Receive data from some sender (typically from a network).
+// - Push received data to the pipeline by calling nextConsumer.Consume*() function.
+// - Acknowledge successful data receipt to the sender if Consume*() succeeded or
+//   return a failure to the sender if Consume*() returned an error.
+// This ensures there are strong delivery guarantees once the data is acknowledged
+// by the Collector.
 type Receiver interface {
 	Component
 }