MM-13838 Bypass the HTTP client when getting image dimensions from the image proxy (#10208)

* MM-13838 Bypass the HTTP client when getting image dimensions from the proxy

* Add additional log messages to debug failing test

* Fix unit test to work on Jenkins

services/imageproxy/error.go

@@ -0,0 +1,8 @@
+// Copyright (c) 2017-present Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package imageproxy
+
+type Error struct {
+	error
+}