MM-11272 Add OpenGraph and image dimension metadata to posts (#9313)

* Move OpenGraph code into its own file

* Move OpenGraph image proxying to app layer

* Move test file code out of api4 package

* MM-11272 Add OpenGraph and image dimension metadata to posts

model/post.go

@@ -93,8 +93,8 @@ type Post struct {
 
 type PostImageDimensions struct {
 	URL    string `json:"url"`
-	Width  int64  `json:"width"`
-	Height int64  `json:"height"`
+	Width  int    `json:"width"`
+	Height int    `json:"height"`
 }
 
 type PostEphemeral struct {