Add platform config to proxy plugins

Signed-off-by: Derek McGowan <derek@mcg.dev>

services/server/config/config.go

@@ -167,8 +167,9 @@ type CgroupConfig struct {
 
 // ProxyPlugin provides a proxy plugin configuration
 type ProxyPlugin struct {
-	Type    string `toml:"type"`
-	Address string `toml:"address"`
+	Type     string `toml:"type"`
+	Address  string `toml:"address"`
+	Platform string `toml:"platform"`
 }
 
 // Decode unmarshals a plugin specific configuration by plugin id