ui: Add subcommand to initialize a new local pallet

[ethanjli]

Currently, the Forklift CLI provides no way to initialize a new local pallet; that must instead be done using the Git CLI with git init (or some other Git tool) and by manually creating files (e.g. for forklift-pallet.yml). It would be nice if we could provide a CLI (and maybe also a simple TUI using https://github.com/charmbracelet/huh) to make it easier to initialize a new local pallet, e.g. via the plt init subcommand. It would also be great if the TUI could provide an initialization wizard to add any external package repos and package deployments needed by the user.

It would also make sense to make this subcommand work for dev plt init.

This functionality will become much more useful after we complete #253.

[ethanjli]

Part of the initialization flow could be an option to set up the local pallet as an override over an existing pallet (for customization), by setting up a requirement for that existing pallet, and maybe also some sort of local update-checking mechanism (or auto-upgrade mechanism) for that requirement (though it may be simpler/safer to just shift the responsibility of such auto-upgrades onto a remote host for the pallet, as in #242 with GitHub CI; in that case, we'd want to implement #233 with starter configs for auto-upgrading dependencies).