MM-14030 Add format and frame count to image metadata (#10757)

* MM-14030 Add initial CountFrames

* MM-14030 Add format and frame count to image metadata

* Fix tests and stop using image dimensions from OpenGraph

* Fix copyright header

* Move license to NOTICE.txt

model/post_metadata.go

@@ -31,6 +31,12 @@ type PostMetadata struct {
 type PostImage struct {
 	Width  int `json:"width"`
 	Height int `json:"height"`
+
+	// Format is the name of the image format as used by image/go such as "png", "gif", or "jpeg".
+	Format string `json:"format"`
+
+	// FrameCount stores the number of frames in this image, if it is an animated gif. It will be 0 for other formats.
+	FrameCount int `json:"frame_count"`
 }
 
 func (o *PostImage) ToJson() string {