[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

vendor/github.com/dsoprea/go-utility/v2/filesystem/does_exist.go

@@ -1,19 +0,0 @@
-package rifs
-
-import (
-	"os"
-)
-
-// DoesExist returns true if we can open the given file/path without error. We
-// can't simply use `os.IsNotExist()` because we'll get a different error when
-// the parent directory doesn't exist, and really the only important thing is if
-// it exists *and* it's readable.
-func DoesExist(filepath string) bool {
-	f, err := os.Open(filepath)
-	if err != nil {
-		return false
-	}
-
-	f.Close()
-	return true
-}