Let Tendermint p2p addresses be specified by hostname as well as by IP for genesis validators

[james-chf]

When calling namadac utils init-genesis-validator, and in the network config/genesis file, validators' net_addresses are specified in the format {ip:port} e.g.

net_address = "1.2.3.4:26656"

It should be possible to also be able to specify this using a hostname instead of an IP e.g. `"example.com:26656" (https://github.com/informalsystems/tendermint-rs/blob/035acabeb4139454fea03c467f14d007feb1294c/config/src/net.rs#L30-L39).

Note that this net_address config value is used internally for some fields which may need an {ip:port}, for those cases we may need to split out this config value (or resolve the hostname via DNS to an IP address, only where appropriate)

[james-chf]

One big advantage to supporting this is that it would be easier to spin up a local chain with multiple Namada nodes using something like Docker Compose, where each Namada node could run on a predictably named host e.g. namada-1:26656, namada-2:26656, ...