docs: add vendored GStreamer LGPL files to third-party-programs.txt

List 6 source files originating from upstream GStreamer that are
included in the repository under LGPL-2.0-or-later license:

- gstanalyticsgroupmtd.{h,c} (Copyright Collabora Ltd)
- gstanalyticskeypointmtd.{h,c} (Copyright Collabora)
- gstvideometa_matrix.{h,c} (Copyright Wim Taymans)

These files retain their original LGPL headers and must not be
relicensed to MIT.

Author: OskarFiedot

third-party-programs.txt

@@ -724,5 +724,37 @@ THE SOFTWARE.
 This software depends on the fmt lib (MIT License),
 and users must comply to its license: https://github.com/fmtlib/fmt/blob/master/LICENSE.rst
 
+-------------------------------------------------------------
+
+8. GStreamer Analytics and Video Meta (vendored source files)
+    Copyright (C) 2025 Collabora Ltd
+        @author: Daniel Morin <daniel.morin@collabora.com>
+    Copyright (C) 2026 Collabora
+        @author: Daniel Morin <daniel.morin@collabora.com>
+    Copyright (C) 2011 Wim Taymans <wim.taymans@gmail.com>
+
+    Files:
+        include/dlstreamer/gst/metadata/gstanalyticsgroupmtd.h
+        include/dlstreamer/gst/metadata/gstanalyticskeypointmtd.h
+        include/dlstreamer/gst/metadata/gstvideometa_matrix.h
+        src/gst/metadata/gstanalyticsgroupmtd.c
+        src/gst/metadata/gstanalyticskeypointmtd.c
+        src/gst/metadata/gstvideometa_matrix.c
+
+    This library is free software; you can redistribute it and/or
+    modify it under the terms of the GNU Library General Public
+    License as published by the Free Software Foundation; either
+    version 2 of the License, or (at your option) any later version.
+
+    This library is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+    Library General Public License for more details.
+
+    You should have received a copy of the GNU Library General Public
+    License along with this library; if not, write to the
+    Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
+    Boston, MA 02110-1301, USA.
+
 -------------------------------------------------------------
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