## Issue Addressed
#1378
## Proposed Changes
Boot node reuses code from beacon_node to initialize network config. This also enables using the network directory to store/load the enr and the private key.
## Additional Info
Note that before this PR the port cli arguments were off (the argument was named `enr-port` but used as `boot-node-enr-port`).
Therefore as port always the cli port argument was used (for both enr and listening). Now the enr-port argument can be used to overwrite the listening port as the public port others should connect to.
Last but not least note, that this restructuring reuses `ethlibp2p::NetworkConfig` that has many more options than the ones used in the boot node. For example the network config has an own `discv5_config` field that gets never used in the boot node and instead another `Discv5Config` gets created later in the boot node process.
Co-authored-by: Age Manning <Age@AgeManning.com>
