Add in-place-testnet command (#561) ## Describe your changes and provide context (sei-chain PR: https://github.com/sei-protocol/sei-chain/pull/2063) To use: 1. modify `~/.sei/config/config.toml`: change `mode` to `validator` and turn off statesync 2. run `seid in-place-testnet <some new chain id name e.g. localsei> ## Testing performed to validate your change