Backpropagate Cargo.lock updates to all lock files (#9180)

* Experiment to backpropagate Cargo.lock updates to all lock files

* Move most of dependabot-specific code to its own file

* Various cleanups

* Fine tune..

* Clean up shells and stop obscure API...

ci/dependabot-pr.sh

@@ -0,0 +1,36 @@
+#!/usr/bin/env bash
+
+set -ex
+
+cd "$(dirname "$0")/.."
+
+if ! echo "$BUILDKITE_BRANCH" | grep -E '^pull/[0-9]+/head$'; then
+  echo "not pull request!?" >&2
+  exit 1
+fi
+
+source ci/rust-version.sh stable
+
+ci/docker-run.sh $rust_nightly_docker_image ci/dependabot-updater.sh
+
+if [[ $(git status --short :**/Cargo.lock | wc -l) -eq 0 ]]; then
+  echo --- ok
+  exit 0
+fi
+
+echo --- "(FAILING) Backpropagating dependabot-triggered Cargo.lock updates"
+
+name="dependabot-buildkite"
+api_base="https://api.github.com/repos/solana-labs/solana/pulls"
+pr_num=$(echo "$BUILDKITE_BRANCH" | grep -Eo '[0-9]+')
+branch=$(curl -s "$api_base/$pr_num" | python -c 'import json,sys;print json.load(sys.stdin)["head"]["ref"]')
+
+git add :**/Cargo.lock
+EMAIL="dependabot-buildkite@noreply.solana.com" \
+  GIT_AUTHOR_NAME="$name" \
+  GIT_COMMITTER_NAME="$name" \
+  git commit -m "[auto-commit] Update all Cargo lock files"
+git push origin "HEAD:$branch"
+
+echo "Source branch is updated; failing this build for the next"
+exit 1