Change ffmpeg handling (#4688)

* Make ffmpeg/ffprobe settable and remove auto download
* Detect when ffmpeg not present in setup
* Add download ffmpeg task
* Add download ffmpeg button in system settings
* Download ffmpeg during setup

internal/api/resolver_query_configuration.go

@@ -91,6 +91,8 @@ func makeConfigGeneralResult() *ConfigGeneralResult {
 		CachePath:                     config.GetCachePath(),
 		BlobsPath:                     config.GetBlobsPath(),
 		BlobsStorage:                  config.GetBlobsStorage(),
+		FfmpegPath:                    config.GetFFMpegPath(),
+		FfprobePath:                   config.GetFFProbePath(),
 		CalculateMd5:                  config.IsCalculateMD5(),
 		VideoFileNamingAlgorithm:      config.GetVideoFileNamingAlgorithm(),
 		ParallelTasks:                 config.GetParallelTasks(),