analytics: send report without loading it to memory

shout-out to @Suor for the suggestion

dvc/analytics.py

@@ -52,11 +52,10 @@ def is_enabled():
 
 def send(path):
     url = "https://analytics.dvc.org"
+    headers = {"content-type": "application/json"}
 
     with open(str(path)) as fobj:
-        report = json.load(fobj)
-
-    requests.post(url, json=report, timeout=5)
+        requests.post(url, data=fobj, headers=headers, timeout=5)
 
 
 def scm_in_use():

tests/unit/test_analytics.py

@@ -34,7 +34,8 @@ def test_send(mock_post, tmp_path):
 
     fname.write_text(str(json.dumps(report)))
     analytics.send(fname)
-    mock_post.assert_called_with(url, json=report, timeout=5)
+    assert mock_post.called
+    assert mock_post.call_args.args[0] == url
 
 
 @pytest.mark.parametrize(