feat(merod): implement generic config edit

[fbozic]

Implement a more generic config edit solution. Interface similar to docker build-arg pattern.
Examples of string, number, and bool args:

cargo run -p merod -- --node-name node1 config \
  --arg=context.config.new.contract_id='"myamestrov.testnet"' \
  --arg=sync.timeout_ms=20000 \
  --arg=discovery.mdns=false

[miraclx]

Suggested change

#[clap(short, long, value_parser = value_parser!(KeyValuePair))]

You should be able to skip value_parser as T: FromStr is implied. Also, can we skip the --arg flag?