@spec get(t(), atom(), any()) :: any()

Gets the key value from the configuration.

If not found, it'll fall back to environment config, and lastly to the default value which is nil if not specified.

@spec merge(t(), t()) :: t()

Merges two configurations.

@spec put(t(), atom(), any()) :: t()

Puts a new key value to the configuration.

@spec raise_error(binary()) :: no_return()

Raise a ConfigError exception.

@spec repo!(t()) :: atom()

Retrieves the repo module from the config, or raises an exception.

@spec user!(t()) :: atom()

Retrieves the user schema module from the config, or raises an exception.