Automate release procedure

[akrejcir]

Create a script for creating github release, so we don't forget any of the steps.

For new major release:

• Create a new release-vX.Y branch from main.
• Create a tag vX.Y.Z on release-vX.Y branch.
• Create Github release from this tag. It's important to set target_commitish to release-vX.Y branch. CI uses it.
• Create an annotated tag api/vX.Y.Z pointing to the same commit as vX.Y.Z. This is needed to make the api submodule accessible.
• Post a PR to https://github.com/openshift/release repository to activate CI for the new release-vX.Y branch.

For new minor release:

• The same steps as above, but without creating a new branch and creating PR to https://github.com/openshift/release .