[Access] Change SendAndSubscribe endpoint's MessageIndex to start at 0

[peterargue]

Problem Definition

The SendAndSubscribeTransactionStatuses endpoints includes a MessageIndex field to help the client check that they received all messages. Currently, this value starts at 1 instead of 0, which is a little confusing since almost all iteration fields start at 0, and it's documented that it starts at 0.
https://github.com/onflow/flow/blob/0b0946dbb2683cec184522b0e3e88246b076a2dc/protobuf/flow/access/access.proto#L753-L754

Other endpoints are documented to start at 1, but actually start at 0:
https://github.com/onflow/flow/blob/0b0946dbb2683cec184522b0e3e88246b076a2dc/protobuf/flow/executiondata/executiondata.proto#L469-L470
https://github.com/onflow/flow/blob/0b0946dbb2683cec184522b0e3e88246b076a2dc/protobuf/flow/executiondata/executiondata.proto#L621-L622

Proposed Solution

Let's update the logic and docs to use 0 as the first value for all endpoints.

This is the current logic for SendAndSubscribeTransactionStatuses

flow-go/access/handler.go

Lines 1435 to 1450 in 0dde730

	messageIndex := counters.NewMonotonousCounter(0)
	return subscription.HandleSubscription(sub, func(txResults []*TransactionResult) error {
	for i := range txResults {
	value := messageIndex.Increment()
	err = stream.Send(&access.SendAndSubscribeTransactionStatusesResponse{
	TransactionResults: TransactionResultToMessage(txResults[i]),
	MessageIndex: value,
	})
	if err != nil {
	return rpc.ConvertError(err, "could not send response", codes.Internal)
	}
	}
	return nil
	})

We could update it to be similar to the logic in other endpoints

flow-go/engine/access/state_stream/backend/handler.go

Lines 417 to 427 in f6814f8

	index := messageIndex.Value()
	if ok := messageIndex.Set(index + 1); !ok {
	return status.Errorf(codes.Internal, "message index already incremented to %d", messageIndex.Value())
	}
	err = send(&executiondata.SubscribeAccountStatusesResponse{
	BlockId: convert.IdentifierToMessage(resp.BlockID),
	BlockHeight: resp.Height,
	Results: results,
	MessageIndex: index,
	})

[illia-malachyn]

If you run new examples onflow/flow-go-sdk#794 via make stream-account-statuses, you will run into an error msg received out of order. The current implementation expects it to start from 0, but it actually starts from 1 even though the tests expect it to start from zero. So, this is the bug and it has to be fixed asap