add config path override

[HenryYYang]

What changed? Why?

Add 2 env var overrides that allows for loading the config from file.

• CHAINSTORAGE_CONFIG_ROOT specifies the file directory path where config directory is located. This allow loading the config for different networks for admins
• CHAINSTORAGE_CONFIG_PATH specifies the file path for the config file to load. This allow loading a specific config file for the current server or worker.

How did you test the change?

• [X] unit test
• [ ] integration test
• [ ] functional test
• [ ] adhoc test (described below)