Add a file to get the current latest version.

[iamsurfing]

What would you like to be added:

Add a file to get the current latest version like this.

curl https://pkgs.k8s.io/core:/stable:/latest.txt
v1.30

Why is this needed:

CI/CD can always use the latest version.

[saschagrunert]

@iamsurfing how about using https://dl.k8s.io/release/stable.txt ?

[iamsurfing]

It is OK in Internet, but it is not good while using mirror.

container--->mirror1--->dl.k8s.io
container--->mirror2--->pkgs.k8s.io

If mirror1 sync successful but mirror2 sync failed, the build will failed. It is more obvious in enterprise.

Add the file can make build script more robust.