Add an `appd config` subcommand

[fadeev]

Before we abstracted away the CLI implementation it used to be possible to change CLI config values, like default keyring backend. Since the SDK has switched back to having client.toml as a config CLI, we should add this functionality to Starport.

Related:

• Add client config subcommand to CLI cosmos/cosmos-sdk#8953
• https://github.com/cosmos/cosmos-sdk/blob/b4d1a5e5d6c9393c02c69fcbd34e9fd7ef4e0879/client/config/config.go
• https://github.com/cosmos/gaia/blob/v5.0.2/cmd/gaiad/cmd/root.go#L58

[lumtis]

This will be a feature to add to https://github.com/tendermint/spm