Disentangle nested configuration files

[netsensei]

Detailed description

The config_*.yml files are currently nested into each other.

• There's a main config.yml file which is included in config_test.yml and config_dev.yml
• config_dev.yml is loaded in config_test.yml
• There's a main security.yml file which is loaded in config.yml
• There's a routing.yml and a routing_dev.yml
• etc.

This setup is brittle, causes confusing and is error prone. Creating a separate security_test.yml and including it in config_test.yml, doesn't correctly override the main firewall in security.yml higher up the include chain, for instance.

Context

This is important to allow clean functional and unit testing. And it's important because isolating concerns creates a less room for errors and bugs.

Possible implementation

• The configuration files should be completely split up, and tailored to their specific environments: test, dev and production.
• The configuration files need to be cleaned up and documented.