[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/cleaner/media_test.go

@@ -373,13 +373,13 @@ func (suite *MediaTestSuite) TestUncacheAndRecache() {
 	suite.True(storage.IsNotFound(err))
 
 	// now recache the image....
-	data := func(_ context.Context) (io.ReadCloser, int64, error) {
+	data := func(_ context.Context) (io.ReadCloser, error) {
 		// load bytes from a test image
 		b, err := os.ReadFile("../../testrig/media/thoughtsofdog-original.jpg")
 		if err != nil {
 			panic(err)
 		}
-		return io.NopCloser(bytes.NewBuffer(b)), int64(len(b)), nil
+		return io.NopCloser(bytes.NewBuffer(b)), nil
 	}
 
 	for _, original := range []*gtsmodel.MediaAttachment{