Docker: Override NetworkName/NodeConfigFile if DB_SYNC_CONFIG is specified

> **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](https://github.com/IntersectMBO/cardano-db-sync/issues/1942#issuecomment-2663116771)_