obs-ffmpeg: Improve color space handling

Add support for VIDEO_CS_SRGB.

Use SMPTE 170M for 601 instead of undef/BT470BG. This is the
American/Chromium way of handling 601.

Add color metadata to the container file as well via ffmpeg-mux.

plugins/obs-ffmpeg/obs-ffmpeg-output.h

@@ -23,7 +23,9 @@ struct ffmpeg_cfg {
 	int audio_tracks;
 	enum AVPixelFormat format;
 	enum AVColorRange color_range;
-	enum AVColorSpace color_space;
+	enum AVColorPrimaries color_primaries;
+	enum AVColorTransferCharacteristic color_trc;
+	enum AVColorSpace colorspace;
 	int scale_width;
 	int scale_height;
 	int width;