Add a command in CLI to generate ENR

[GrapeBaBa]

Original from TG discussion.

CLI design:

zeam enr gen --sk 0x1234567890abcdef... --udp 30303 --ip 192.168.1.100 --tcp 30304

@g11tech Is it like that

[GrapeBaBa]

After weekly meeting, we should create a separate CLI for this right now.