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/options.go

@@ -76,6 +76,7 @@ func ServerConnector(s *Server) AppOption {
 		a.Saml = s.Saml
 
 		a.HTTPService = s.HTTPService
+		a.ImageProxy = s.ImageProxy
 		a.Timezones = s.timezones
 	}
 }