scorecard: more upload options

`--upload-no-cl` for uploads without "Content-Length:"
`--upload-parallel=1` for testing only serial uploads

Closes #20035

tests/http/testenv/curl.py

@@ -784,6 +784,7 @@ class CurlClient:
                  with_stats: bool = True,
                  with_headers: bool = False,
                  with_profile: bool = False,
+                 suppress_cl: bool = False,
                  extra_args: Optional[List[str]] = None):
         if extra_args is None:
             extra_args = []
@@ -798,6 +799,11 @@ class CurlClient:
             extra_args.extend([
                 '-w', '%{json}\\n'
             ])
+        if suppress_cl:
+            extra_args.extend([
+                '-H', 'Content-Length:',
+                '-H', 'Transfer-Encoding: chunked',
+            ])
         return self._raw(urls, intext=data,
                          alpn_proto=alpn_proto, options=extra_args,
                          with_stats=with_stats,