Adding interplugin communication. (#12829)

* Adding interplugin communication.

* Naming changes and moving ResponseTransfer to own file.

* Fix.

* Tests and moving to buffering bytes.

* Switching API to passing plugin ID through path rather than a header.

* Review feedback.

plugin/interface_generator/main.go

@@ -392,17 +392,18 @@ func getPluginPackageDir() string {
 func removeExcluded(info *PluginInterfaceInfo) *PluginInterfaceInfo {
 	toBeExcluded := func(item string) bool {
 		excluded := []string{
-			"OnActivate",
+			"FileWillBeUploaded",
 			"Implemented",
 			"LoadPluginConfiguration",
-			"ServeHTTP",
-			"FileWillBeUploaded",
-			"MessageWillBePosted",
-			"MessageWillBeUpdated",
 			"LogDebug",
+			"LogError",
 			"LogInfo",
 			"LogWarn",
-			"LogError",
+			"MessageWillBePosted",
+			"MessageWillBeUpdated",
+			"OnActivate",
+			"PluginHTTP",
+			"ServeHTTP",
 		}
 		for _, exclusion := range excluded {
 			if exclusion == item {