ui: Enable initialization of a new GitHub repo for the local pallet

[ethanjli]

Currently, the only way to make a new pallet on GitHub is to either fork an existing pallet on GitHub or manually create a local pallet (as described in #232) and then use the GitHub web interface with the Git CLI (or some other Git tool, such as the GitHub CLI) to link the local pallet with a remote repo on GitHub. It would be nice if our CLI could provide an easy way for users to initialize a new repo on GitHub for their local pallet (as part of the subcommand to be added by #232, where the subcommand will skip Git repo initialization steps and proceed directly to GitHub repo initialization if the local pallet is already a Git repo). It could also be nice to add a --fork flag (or maybe a separate plt fork subcommand) which will make the subcommand create a GitHub fork of the existing repo (if it already exists), update the pallet path in the forklift-pallet.yml file (and the forklift-repository.yml file, if exists), and update the origin remote.

It would be great if the repo could be created with forklift-pallet as a topic tag. Also, maybe we can wrap https://github.com/cli/cli or https://github.com/cli/go-gh to implement this functionality.

This functionality will become much more useful after #253, and especially together with #232.