feat(config): support dingo.yaml config file loading with env overrides in dingo

[arepala-uml]

1. Added --config flag in cmd/dingo to make sure of custom configuration file as input.
2. Added proper yaml tags on all fields in the dingo Config struct to enable unmarshaling from YAML.
3. Implemented logic to load configuration from YAML first, and then override with environment variables
4. Updated node.Run() to accept loaded config from main instead of reloading internally.
5. Wrote unit tests to validate config loading with and without a YAML file.
6. Executed the cmd/dingo/main.go with and without config file as input and it is working fine.

Closes #529

[agaffney]

This looks great. I had just one minor comment