Return 400 instead of 500 on incorrect OTLP payload (#6599)

## Which problem is this PR solving?
- Resolves #6598 

## Description of the changes
- Changed StatusInternalServerError to StatusBadRequest because
otlp2traces doing the unmarshaling will go into error if there is error
in the payload
- Added a new unit test for the change

## How was this change tested?
- make lint test => pass 

## Checklist
- [x] I have read
https://github.com/jaegertracing/jaeger/blob/master/CONTRIBUTING_GUIDELINES.md
- [x] I have signed all commits
- [x] I have added unit tests for the new functionality
- [x] I have run lint and test steps successfully
  - for `jaeger`: `make lint test`
  - for `jaeger-ui`: `npm run lint` and `npm run test`

---------

Signed-off-by: cs-308-2023 <[email protected]>
Signed-off-by: Yuri Shkuro <[email protected]>
Co-authored-by: Yuri Shkuro <[email protected]>
Co-authored-by: Yuri Shkuro <[email protected]>

Author: ADI-ROXX

cmd/query/app/http_handler.go

@@ -183,7 +183,7 @@ func (aH *APIHandler) transformOTLP(w http.ResponseWriter, r *http.Request) {
 	}
 
 	traces, err := otlp2traces(body)
-	if aH.handleError(w, err, http.StatusInternalServerError) {
+	if aH.handleError(w, err, http.StatusBadRequest) {
 		return
 	}
 

cmd/query/app/http_handler_test.go

@@ -769,6 +769,15 @@ func TestTransformOTLPBadPayload(t *testing.T) {
 	}, querysvc.QueryServiceOptions{})
 }
 
+func TestBadOTLPReturns400(t *testing.T) {
+	withTestServer(t, func(ts *testServer) {
+		err := postJSON(ts.server.URL+"/api/transform", "Bad Payload", nil)
+		var httpErr *HTTPError
+		require.ErrorAs(t, err, &httpErr)
+		require.Equal(t, 400, httpErr.StatusCode)
+	}, querysvc.QueryServiceOptions{})
+}
+
 func TestGetMetricsSuccess(t *testing.T) {
 	mr := &metricsmocks.Reader{}
 	apiHandlerOptions := []HandlerOption{
@@ -980,6 +989,15 @@ func postJSON(url string, req any, out any) error {
 	return execJSON(r, make(map[string]string), out)
 }
 
+type HTTPError struct {
+	StatusCode int
+	Body       string
+}
+
+func (e *HTTPError) Error() string {
+	return fmt.Sprintf("%d error from server: %s", e.StatusCode, e.Body)
+}
+
 // execJSON executes an http request against a server and parses response as JSON
 func execJSON(req *http.Request, additionalHeaders map[string]string, out any) error {
 	req.Header.Add("Accept", "application/json")
@@ -999,7 +1017,10 @@ func execJSON(req *http.Request, additionalHeaders map[string]string, out any) e
 		if err != nil {
 			return err
 		}
-		return fmt.Errorf("%d error from server: %s", resp.StatusCode, body)
+		return &HTTPError{
+			StatusCode: resp.StatusCode,
+			Body:       string(body),
+		}
 	}
 
 	if out == nil {