Here is the logic to determine which `config.json` file will be used:
1. from command line option: `--config myConfig.json`
2. `$HOME/.xds/config.json` file
-3. `<xds-server executable dir>/config.json` file
+3. `<current dir>/config.json` file
+4. `<xds-server executable dir>/config.json` file
Supported fields in configuration file are:
```json
// Order to determine which config file is used:
// 1/ from command line option: "--config myConfig.json"
// 2/ $HOME/.xds/config.json file
-// 3/ <xds-server executable dir>/config.json file
+// 3/ <current_dir>/agent-config.json file
+// 4/ <xds-server executable dir>/config.json file
func updateConfigFromFile(c *Config, confFile string) error {