chore: Improve trace agent error message (#900)

# This PR
Add some details to trace agent error messages.

# Motivation
#899 mentions
the error log:
```
DD_EXTENSION | ERROR | Failed to buffer the request body: length limit exceeded
```
This error message is probably from Rust, not from our extension, and
it's hard to pinpoint where it's logged. My hypothesis is it's from the
two places touched by this PR. Let's add details to the log messages so
if someone sees the same error again, we know where it's from.

Author: lym953

bottlecap/src/traces/trace_agent.rs

@@ -433,7 +433,12 @@ impl TraceAgent {
     ) -> Response {
         let (parts, body) = match extract_request_body(request).await {
             Ok(r) => r,
-            Err(e) => return error_response(StatusCode::INTERNAL_SERVER_ERROR, e),
+            Err(e) => {
+                return error_response(
+                    StatusCode::INTERNAL_SERVER_ERROR,
+                    format!("TRACE_AGENT | handle_traces | Error extracting request body: {e}"),
+                );
+            }
         };
 
         if let Some(content_length) = parts
@@ -551,7 +556,12 @@ impl TraceAgent {
         debug!("TRACE_AGENT | Proxied request for {context}");
         let (parts, body) = match extract_request_body(request).await {
             Ok(r) => r,
-            Err(e) => return error_response(StatusCode::INTERNAL_SERVER_ERROR, e),
+            Err(e) => {
+                return error_response(
+                    StatusCode::INTERNAL_SERVER_ERROR,
+                    format!("TRACE_AGENT | handle_proxy | Error extracting request body: {e}"),
+                );
+            }
         };
 
         let target_url = format!("https://{}.{}{}", backend_domain, config.site, backend_path);