Refactor web service API to clarify stream and repeated concepts

[charphi]

In GRPC, stream and repeated concepts can be confusing and lead to mistakes. A clarification is needed.

For example, this current method has a problem:

rpc GetAvailability(KeyDimensionRequestDto) returns (stream DimensionCodesDto);

message DimensionCodesDto {
  repeated string codes = 1;
}