obs-ffmpeg: Add missing "FFmpegOpts" locale

plugins/obs-ffmpeg/data/locale/en-US.ini

@@ -1,6 +1,7 @@
 FFmpegOutput="FFmpeg Output"
 FFmpegAAC="FFmpeg Default AAC Encoder"
 FFmpegOpus="FFmpeg Opus Encoder"
+FFmpegOpts="FFmpeg Options"
 Bitrate="Bitrate"
 MaxBitrate="Max Bitrate"
 Preset="Preset"