Truncate data from OpenGraph metadata (#10532)

* Truncate strings from OpenGraph metada

* remove unwanted opengraph fields, limit to 1 image

* test helper functions

* Add truncating test

* fix typo

* change test into not comparing for the pointer value

* truncate only once

* only shorten fields that were already present

* set maximum of 5 images

* fix original tests

* fix test

* limit to 5 images

* fix typo

* place functions below types, simplify function commentaries

* Rewrite how to empty opengraph's structure

app/post_metadata.go

@@ -379,6 +379,7 @@ func (a *App) getLinkMetadata(requestURL string, timestamp int64, isNewPost bool
 		// Parse the data
 		og, image, err = a.parseLinkMetadata(requestURL, body, contentType)
 	}
+	og = model.TruncateOpenGraph(og) // remove unwanted length of texts
 
 	// Write back to cache and database, even if there was an error and the results are nil
 	cacheLinkMetadata(requestURL, timestamp, og, image)