add cargo-update-and-push script

Author: gburgessiv

scripts/cargo-update-and-push.sh

@@ -0,0 +1,23 @@
+#!/bin/bash -eu
+# Runs `cargo update`, runs local tests, pushes w/ automerge on success.
+
+cd "$(dirname "$(readlink -m "$0")")/.."
+
+if [[ -n "$(git status --porcelain)" ]]; then
+  echo "There are uncommitted changes" >&2
+  exit 1
+fi
+
+cargo update
+cargo test
+git commit -a -m 'Run cargo-update'
+git checkout -B cargo-update
+git push --set-upstream github HEAD:cargo-update
+
+pr_url=$(gh pr create \
+  --title='Run cargo-update' \
+  --body='Autogenerated by cargo-update-and-push.sh.')
+echo "Posted update PR as ${pr_url}."
+
+gh pr merge "${pr_url}" --auto --delete-branch --squash
+echo "Set autosubmit."