Automate release changes (#7929)

packaging/cut_release.sh

+#!/usr/bin/env bash
+#
+# Usage (run from root of project):
+# TEST_INFRA_BRANCH=release/2.1 RELEASE_BRANCH=release/2.1 RELEASE_VERSION=2.1.0 packaging/cut_release.sh
+#
+# TEST_INFRA_BRANCH: The release branch of test-infra that houses all reusable
+# workflows
+#
+# RELEASE_BRANCH: The name of the release branch for this repo
+#
+# RELEASE_VERSION: Version of this current release
+
+set -eou pipefail
+
+# Create and Check out to Release Branch
+git checkout -b "${RELEASE_BRANCH}"
+
+# Change all GitHub Actions to reference the test-infra release branch
+# as opposed to main.
+for i in .github/workflows/*.yml; do 
+  if [[ "$OSTYPE" == "darwin"* ]]; then
+    sed -i '' -e s#@main#@"${TEST_INFRA_BRANCH}"# $i;
+    sed -i '' -e s#test-infra-ref:[[:space:]]main#"test-infra-ref: ${TEST_INFRA_BRANCH}"# $i;
+  else
+    sed -i -e s#@main#@"${TEST_INFRA_BRANCH}"# $i;
+    sed -i -e s#test-infra-ref:[[:space:]]main#"test-infra-ref: ${TEST_INFRA_BRANCH}"# $i;
+  fi
+done
+
+# Update the Release Version in version.txt
+echo "${RELEASE_VERSION}" >version.txt
+
+# Optional
+# git add ./github/workflows/*.yml version.txt
+# git commit -m "[RELEASE-ONLY CHANGES] Branch Cut for Release {RELEASE_VERSION}"
+# git push origin "${RELEASE_BRANCH}"