MM-10417 Add local image proxy and enable by default (#9967)

* MM-10417 Add local image proxy and enable by default

* Remove unused function

* Add dependencies for willnorris/imageproxy

* Fixed compilation errors

* Lock to the master version of willnorris/imageproxy

* Fix atmos/camo proxy when no SiteURL is specified

* Re-add default values for deprecated settings

* Fix unit tests added by merge

* Pass imageproxy to App struct

* Remove unneeded locking when creating the image proxy

* Remove empty test file

app/post_metadata.go

@@ -25,8 +25,10 @@ var linkCache = utils.NewLru(LINK_CACHE_SIZE)
 func (a *App) InitPostMetadata() {
 	// Dump any cached links if the proxy settings have changed so image URLs can be updated
 	a.AddConfigListener(func(before, after *model.Config) {
-		if (before.ServiceSettings.ImageProxyType != after.ServiceSettings.ImageProxyType) ||
-			(before.ServiceSettings.ImageProxyURL != after.ServiceSettings.ImageProxyURL) {
+		if (before.ImageProxySettings.Enable != after.ImageProxySettings.Enable) ||
+			(before.ImageProxySettings.ImageProxyType != after.ImageProxySettings.ImageProxyType) ||
+			(before.ImageProxySettings.RemoteImageProxyURL != after.ImageProxySettings.RemoteImageProxyURL) ||
+			(before.ImageProxySettings.RemoteImageProxyOptions != after.ImageProxySettings.RemoteImageProxyOptions) {
 			linkCache.Purge()
 		}
 	})