Add the cherry-pick script as a hack command

hack/cherry-pick.sh

@@ -0,0 +1,111 @@
+#!/usr/bin/env bash
+
+# Copyright 2022 The PipeCD Authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+set -o errexit
+set -o nounset
+set -o pipefail
+
+QUIET='false'
+CLEANUP_BRANCH='false'
+while getopts 'qc' opt; do
+  case $opt in
+    q)
+      QUIET='true' ;;
+    c)
+      CLEANUP_BRANCH='true' ;;
+    ?)
+      echo "Usage: hack/cherry-pick.sh [-q] [-c] <branch> <pull-requests>" >&2
+      exit 1 ;;
+  esac
+done
+shift "$(($OPTIND -1))"
+
+BRANCH=$1; shift 1
+PULL_REQUESTS=($@)
+
+# Check gh authentication
+echo "+++ Checking gh authentication..."
+gh auth status
+
+COMMIT_HASHS=()
+for pull in "${PULL_REQUESTS[@]}"; do
+  hash="$(gh pr view ${pull} --json mergeCommit --jq .mergeCommit.oid)"
+  COMMIT_HASHS+=($hash)
+done
+
+function join { local IFS="$1"; shift; echo "$*"; }
+PULL_DASH=$(join - "${PULL_REQUESTS[@]/#/#}")
+PULL_SUBJ=$(join " " "${PULL_REQUESTS[@]/#/#}")
+NEWBRANCH="cherry-pick-${PULL_DASH}-to-${BRANCH}"
+
+# Update all remote branches
+echo "+++ Updating remote branches..."
+git remote update
+echo
+
+# Create local branch
+echo "+++ Creating a local branch..."
+git checkout -b ${NEWBRANCH} "origin/${BRANCH}"
+echo
+
+# Cherry-pick pull requests
+COMMITS=$(join " " "${COMMIT_HASHS[@]}")
+echo "+++ Cherry-picking pull requests"
+git cherry-pick ${COMMITS}
+echo
+
+# Check whether to push commits and create a pull request or not
+if ! ${QUIET}; then
+  read -p "+++ Do you push commits and create a pull request? [y/n] " -r
+  if ! [[ "${REPLY}" =~ ^[yY]$  ]]; then
+    echo "Skipped." >&2
+    exit 0
+  fi
+fi
+
+# Push commits to remote branch
+echo "+++ Pushing commits to remote branch..."
+git push origin ${NEWBRANCH}
+echo
+
+# Create a pull request
+echo "+++ Creating a pull request..."
+pull_title="Cherry-pick ${PULL_SUBJ}"
+pull_body=$(cat <<EOF
+**What this PR does / why we need it**:
+Cherry pick of ${PULL_SUBJ}.
+
+**Which issue(s) this PR fixes**:
+
+Fixes #
+
+**Does this PR introduce a user-facing change?**:
+<!--
+If no, just write "NONE" in the release-note block below.
+-->
+\`\`\`release-note
+
+\`\`\`
+EOF
+)
+gh pr create --title="${pull_title}" --body="${pull_body}" --head "${NEWBRANCH}" --base "${BRANCH}"
+
+# Delete a working branch
+if ${CLEANUP_BRANCH}; then
+  echo "+++ Deleting a working branch..."
+  git checkout -
+  git branch -D ${NEWBRANCH}
+if