Helper scripts for kpt repository.

• Generates LICENSES.txt file for kpt release, which includes the licenses of the transitive dependencies of kpt.
• Generates lib.zip, which is a package of source files necessary to satisfy the Mozilla license.

From top-level kpt directory:

./scripts/create-licenses.sh

This script will generate files LICENSES.txt and lib.zip in the top-level directory. These files will eventually be included in the kpt release tarball. This script will first run go mod vendor to generate the vendored dependencies. The script removes the contents of the vendor directory upon success.