Docker: Override NetworkName/NodeConfigFile if DB_SYNC_CONFIG is specified

[sgillespie]

Context : Docker Deployment

Would it be possible to inject these to config file if they are absent?

  "NetworkName": "mainnet",
  "NodeConfigFile": "/nix/store/kcl7gc0q0w70c51lnfh1cdk70niylshd-config-mainnet.json",

All I need is to add few extra insert_options. In order to do that, I need to find out the main-net config.

Additionally

• I need different configuration file for each network.
• it won't be valid on upgrading.

Suggestion:

• Automatically override NetworkName and NodeConfigFile if NETWORK env variable is present and DB_SYNC_CONFIG is also present.

This will drastically reduce configuration hassle for each network and need to find out node configuration file.

Originally posted by @mesudip in #1942