[feature] support processing of (many) more media types (#3090)

* initial work replacing our media decoding / encoding pipeline with ffprobe + ffmpeg

* specify the video codec to use when generating static image from emoji

* update go-storage library (fixes incompatibility after updating go-iotools)

* maintain image aspect ratio when generating a thumbnail for it

* update readme to show go-ffmpreg

* fix a bunch of media tests, move filesize checking to callers of media manager for more flexibility

* remove extra debug from error message

* fix up incorrect function signatures

* update PutFile to just use regular file copy, as changes are file is on separate partition

* fix remaining tests, remove some unneeded tests now we're working with ffmpeg/ffprobe

* update more tests, add more code comments

* add utilities to generate processed emoji / media outputs

* fix remaining tests

* add test for opus media file, add license header to utility cmds

* limit the number of concurrently available ffmpeg / ffprobe instances

* reduce number of instances

* further reduce number of instances

* fix envparsing test with configuration variables

* update docs and configuration with new media-{local,remote}-max-size variables

internal/config/defaults.go

@@ -71,11 +71,11 @@ var Defaults = Configuration{
 	AccountsAllowCustomCSS:   false,
 	AccountsCustomCSSLength:  10000,
 
-	MediaImageMaxSize:        10 * bytesize.MiB,
-	MediaVideoMaxSize:        40 * bytesize.MiB,
 	MediaDescriptionMinChars: 0,
 	MediaDescriptionMaxChars: 1500,
 	MediaRemoteCacheDays:     7,
+	MediaLocalMaxSize:        40 * bytesize.MiB,
+	MediaRemoteMaxSize:       40 * bytesize.MiB,
 	MediaEmojiLocalMaxSize:   50 * bytesize.KiB,
 	MediaEmojiRemoteMaxSize:  100 * bytesize.KiB,
 	MediaCleanupFrom:         "00:00",        // Midnight.