Mm-20223 Add webp emoji support (#20283)

* Added webp package into app/emoji.go , also added a test

* fixed import order inside emoji.go

* Ran go mod tidy

* Conversion to png for Webp emojis that must be resized is implemented

* Deleted unused import

* Added reading mechanism for webp instead of creating

* fileutils and filepath are used while reading a webp file during test

* Deleted readtestwebp function and put it in emoji_test as requested

* Added webp image upload test inside api4/file_test.go

* Expect image is changed from false to true

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

app/emoji.go

@@ -21,6 +21,7 @@ import (
 	"path"
 
 	"github.com/disintegration/imaging"
+	_ "golang.org/x/image/webp"
 
 	"github.com/mattermost/mattermost-server/v6/model"
 	"github.com/mattermost/mattermost-server/v6/shared/mlog"