Adjust splunk_hec to distinguish decoded and raw bytes received

Similar to #1166 this commit adds a `decoded_bytes_received` so that the telemetry
from this blackhole matches the others in the project, measuring the raw/wire bytes
in `bytes_received`.

Signed-off-by: Brian L. Troutwine <brian.troutwine@datadoghq.com>

lading/src/blackhole/splunk_hec.rs

@@ -96,11 +96,12 @@ async fn srv(
 
     let (parts, body) = req.into_parts();
     let bytes = body.collect().await?.to_bytes();
+    counter!("bytes_received", &metric_labels).increment(bytes.len() as u64);
 
     match crate::codec::decode(parts.headers.get(hyper::header::CONTENT_ENCODING), bytes) {
         Err(response) => Ok(response),
         Ok(body) => {
-            counter!("bytes_received", &*labels).increment(body.len() as u64);
+            counter!("decoded_bytes_received", &metric_labels).increment(body.len() as u64);
 
             let mut okay = Response::default();
             *okay.status_mut() = StatusCode::OK;