Resolve configuration values using enviroment values

[ikhoon]

Central Dogma only statically resolves the configuration file - dogma.json. It could be convenient to override the configuration with environment variables, especially for Docker and cloud infrastructure.

The following syntax is inspired by logback's configuration via environment variables

{
    "dataDir": "${DATA_DIR:-./data}",
    "numRepositoryWorkers": "${NUM_REPOSITORY_WORKERS:-16}",
}