Have a default way to download genesis files

[evan-forbes]

It would be nice if users have to spend less time thinking about which genesis they download and install.

As pointed out in a sync discussion, osmosis acheives this by including the genesis in the binary. This is a good simple option, as users likely have to download the mainnet genesis anyway.

Another option would be to hardcode the hashes of the genesis for each live network in the binary, and add a subcommand that would download, verify the hash of, and then install the genesis of a specific network.

[adlerjohn]

Another option would be to hardcode the hashes of the genesis for each live network in the binary, and add a subcommand that would download, verify the hash of, and then install the genesis of a specific network.

This seems like a decent point in the tradeoff space.

[cmwaters]

I agree with just adding support to download the genesis when init is run

[rootulp]

I briefly explored adding this to the celestia-appd init command but init is defined in Cosmos SDK which makes it (a) more difficult to modify and (b) more likely to break when we pull upstream changes. Given our motivation to minimize the diff with upstream, I think another option worth exploring is adding a unique command to celestia-app (e.g. celestia-appd download-genesis <chain-id>).