Plugins: Refactor call resource API handling (#67234)

Moving call resource API stream handling within plugin management as a utility/wrapper. 

Closes #66889

Co-authored-by: Will Browne <wbrowne@users.noreply.github.com>

pkg/plugins/httpresponsesender/http_response_sender_test.go

@@ -0,0 +1,45 @@
+package httpresponsesender
+
+import (
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/grafana/grafana-plugin-sdk-go/backend"
+	"github.com/stretchr/testify/require"
+)
+
+func TestHTTPResponseSender(t *testing.T) {
+	w := httptest.NewRecorder()
+	sender := New(w)
+	require.NotNil(t, sender)
+
+	headers := http.Header{}
+	headers.Add("X-Custom", "custom")
+	err := sender.Send(&backend.CallResourceResponse{
+		Status:  http.StatusOK,
+		Headers: headers,
+		Body:    []byte("Hello world"),
+	})
+	require.NoError(t, err)
+
+	headers2 := http.Header{}
+	headers2.Add("X-Custom-Two", "custom two")
+	err = sender.Send(&backend.CallResourceResponse{
+		Status:  http.StatusNotFound,
+		Headers: headers2,
+		Body:    []byte("Hello world again"),
+	})
+	require.NoError(t, err)
+
+	resp := w.Result()
+	require.NotNil(t, resp)
+	require.Equal(t, http.StatusOK, resp.StatusCode)
+	require.Equal(t, "custom", resp.Header.Get("X-Custom"))
+	require.Empty(t, resp.Header.Get("X-Custom-Two"))
+	bytes, err := io.ReadAll(resp.Body)
+	require.NoError(t, resp.Body.Close())
+	require.NoError(t, err)
+	require.Equal(t, "Hello worldHello world again", string(bytes))
+}