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.bzl b/build/source_list.bzl
index 0deac7a..c6e4873 100644
--- a/build/source_list.bzl
+++ b/build/source_list.bzl
@@ -1508,6 +1508,7 @@
     "quic/moqt/tools/chat_client_bin.cc",
     "quic/moqt/tools/moqt_client.cc",
     "quic/moqt/tools/moqt_end_to_end_test.cc",
+    "quic/moqt/tools/moqt_ingestion_server_bin.cc",
     "quic/moqt/tools/moqt_server.cc",
 ]
 binary_http_hdrs = [