otelgrpc: Add peer attributes to spans generated by stats handlers

[pellared]

The trace instrumentation implemented in #3002 misses peer attributes.

opentelemetry-go-contrib/instrumentation/google.golang.org/grpc/otelgrpc/stats_handler.go

Lines 78 to 84 in 23181f7

	// TagConn can attach some information to the given context.
	func (h *serverHandler) TagConn(ctx context.Context, info *stats.ConnTagInfo) context.Context {
	span := trace.SpanFromContext(ctx)
	attrs := peerAttr(peerFromCtx(ctx))
	span.SetAttributes(attrs...)
	return ctx
	}

The span returned in TagConn is always noop as TagConn is invoked before TagRPC, therefore the peer attributes are never added to the spans.

Currently seems to be blocked by grpc/grpc-go#6897.

[pellared]

@fatsheep9146 Can you take a look at this issue?

[fatsheep9146]

@fatsheep9146 Can you take a look at this issue?

No problem, please assign to me :)

[pellared]

Currently seems to be blocked by grpc/grpc-go#6897.