Create replacement cherry-pick automation for releases

# Problem

We had previously been using the [GCP Cherry-Pick Bot](https://github.com/apps/gcp-cherry-pick-bot) to automate cherry-picks for releases. Unfortunately this bot has been deprecated.

Investigate and implement an alternative.

# Requirements

Input:
- Git repo
- Git Commit SHA or GitHub PR number
- Base branch

Steps:
- `git checkout release/X.Y` and ensure it's up-to-date with origin
- `git checkout -b your-cherry-pick-branch`
- `git cherry-pick -x `
- Fail on any merge conflicts.
- `git push`
- Create a PR with base `release/X.Y`
- Ensure CI passes

Output:
- Link to PR