ekg.md - Provide default config files

[ghost]

In the 'Monitoring a node with EKG' exercise, step 3, the instructions for copying the configuration.yaml, topology.json and genesis.json files are not ideal.

cfg=configuration/defaults/mainnet-via-fetcher
cp $cfg/configuration.yaml config.yaml
cp $cfg/topology.json .
cp $cfg/genesis.json .

The configuration.yaml file specified requires modification:
Protocol: RealPBFT
RequiresNetworkMagic: RequiresNoMagic

It would be preferable to provide a shortcut to an existing config.yaml file that can be downloaded using wget.