lib: add trace support for client reads and writes

- add `CURL_TRC_READ()` and `CURL_TRC_WRITE()`
- use in generic client writers and readers, as well
  as http headers, chunking and websockets

Closes #13223

lib/headers.c

@@ -361,6 +361,8 @@ static CURLcode hds_cw_collect_write(struct Curl_easy *data,
         (type & CLIENTWRITE_TRAILER ? CURLH_TRAILER :
          CURLH_HEADER)));
     CURLcode result = Curl_headers_push(data, buf, htype);
+    CURL_TRC_WRITE(data, "header_collect pushed(type=%x, len=%zu) -> %d",
+                   htype, blen, result);
     if(result)
       return result;
   }