Log Message:
Update gh to 2.3.0.

We've made a significant change to gh's extension system. Now, extension
authors can work in a precompiled language like Go and ship pre-compiled
binaries of their extensions via release assets.

To get started, run gh extension create.

The gh repo create command now has distinct usages for creating a repository
from scratch and creating one from a local git repository.

Create a new repository on GitHub from scratch and clone it locally with

$ gh repo create myrepo --public --clone

Upload an existing local repository with

$ gh repo create myrepo --source=path/to/repo --public

Other new features

- Add command gh auth setup-git for setting up gh-cli as git cred helper
- Add gh config list
- Add new flag gh secret set --no-store to print the encoded secret
- Adding release download for.zip and .tar.gz archives
- gh repo rename