Hex <-> Bech32 node tool

[thibault-martinez]

[Thoralf-M]

We have such functions in iota.rs https://github.com/iotaledger/iota.rs/blob/25651bee21a13d659e24a66ed7e7173ff65f5582/src/utils.rs#L31, could maybe moved to another crate so it can be reused, when you still plan to add this as node tool