PLT-6358: Server HTTP client improvements (#6980)

* restrict untrusted, internal http connections by default

* command test fix

* more test fixes

* change setting from toggle to whitelist

* requested ui changes

* add isdefault diagnostic

* fix tests

app/post.go

@@ -619,7 +619,7 @@ func GetFileInfosForPost(postId string, readFromMaster bool) ([]*model.FileInfo,
 func GetOpenGraphMetadata(url string) *opengraph.OpenGraph {
 	og := opengraph.NewOpenGraph()
 
-	res, err := utils.HttpClient().Get(url)
+	res, err := utils.HttpClient(false).Get(url)
 	if err != nil {
 		l4g.Error("GetOpenGraphMetadata request failed for url=%v with err=%v", url, err.Error())
 		return og