Introduce MoQT demo ingestion server that writes incoming streams into a directory.

It is possible to test this server against the demo chat client by running a command among the lines of `moqt_ingestion_server /tmp/outdir --alsologtostderr --allow_invalid_track_namespaces --tracks=`.

PiperOrigin-RevId: 612845930
diff --git a/build/source_list.json b/build/source_list.json
index 6fe5adc..6bebbca 100644
--- a/build/source_list.json
+++ b/build/source_list.json
@@ -1511,6 +1511,7 @@
     "quiche/quic/moqt/tools/chat_client_bin.cc",
     "quiche/quic/moqt/tools/moqt_client.cc",
     "quiche/quic/moqt/tools/moqt_end_to_end_test.cc",
+    "quiche/quic/moqt/tools/moqt_ingestion_server_bin.cc",
     "quiche/quic/moqt/tools/moqt_server.cc"
   ],
   "binary_http_hdrs": [