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

config/default.json

@@ -71,9 +71,6 @@
         "ExperimentalEnableDefaultChannelLeaveJoinMessages": true,
         "ExperimentalGroupUnreadChannels": "disabled",
         "ExperimentalChannelOrganization": false,
-        "ImageProxyType": "",
-        "ImageProxyOptions": "",
-        "ImageProxyURL": "",
         "EnableAPITeamDeletion": false,
         "ExperimentalEnableHardenedMode": false,
         "EnableEmailInvitations": false,
@@ -413,5 +410,11 @@
         "ClientDirectory": "./client/plugins",
         "Plugins": {},
         "PluginStates": {}
+    },
+    "ImageProxySettings": {
+        "Enable": true,
+        "ImageProxyType": "local",
+        "RemoteImageProxyURL": "",
+        "RemoteImageProxyOptions": ""
     }
 }