[CI/Build] Add release bot workflow

[zjw49246]

Add automated release workflow for vLLM Production Stack

This PR introduces a GitHub Actions workflow to automate the release process for the vLLM production stack, including both Helm chart and router Docker image releases.

Key Features

• Dual trigger support: Scheduled releases (every Monday at 9:00 AM UTC, can be customized later) and manual workflow dispatch
• Flexible versioning: Support for patch, minor, and major version bumps with manual override capability
• Dry run mode: Test releases without actually publishing
• Automated release notes: Generates changelog from merged PRs between releases
• Version management: Updates Helm chart version in Chart.yaml and creates corresponding Git tags

Workflow Components

1. prepare-release: Handles version bumping, Git tagging, and release preparation
2. release-helm: Publishes Helm charts using chart-releaser-action
3. release-docker: Builds and pushes the router Docker image with multiple tags

Testing & Validation

I have tested this workflow in my forked repository with my own Docker Hub account, successfully completing both Helm releases and router Docker image releases. Here's a sample of the release content.

Implementation Notes

• The workflow updates versions by modifying helm/Chart.yaml using sed commands
• The release schedule, currently set for every Monday at 9:00 AM UTC, can be easily adjusted if needed, but thorough testing is difficult due to time-based constraints.

---

• Make sure the code changes pass the pre-commit checks.
• Sign-off your commit by using -s when doing git commit
• Try to classify PRs for easy understanding of the type of changes, such as [Bugfix], [Feat], and [CI].

Detailed Checklist (Click to Expand)

Thank you for your contribution to production-stack! Before submitting the pull request, please ensure the PR meets the following criteria. This helps us maintain the code quality and improve the efficiency of the review process.

PR Title and Classification

Please try to classify PRs for easy understanding of the type of changes. The PR title is prefixed appropriately to indicate the type of change. Please use one of the following:

• [Bugfix] for bug fixes.
• [CI/Build] for build or continuous integration improvements.
• [Doc] for documentation fixes and improvements.
• [Feat] for new features in the cluster (e.g., autoscaling, disaggregated prefill, etc.).
• [Router] for changes to the vllm_router (e.g., routing algorithm, router observability, etc.).
• [Misc] for PRs that do not fit the above categories. Please use this sparingly.

Note: If the PR spans more than one category, please include all relevant prefixes.

Code Quality

The PR need to meet the following code quality standards:

• Pass all linter checks. Please use pre-commit to format your code. See README.md for installation.
• The code need to be well-documented to ensure future contributors can easily understand the code.
• Please include sufficient tests to ensure the change is stay correct and robust. This includes both unit tests and integration tests.

DCO and Signed-off-by

When contributing changes to this project, you must agree to the DCO. Commits must include a Signed-off-by: header which certifies agreement with the terms of the DCO.

Using -s with git commit will automatically add this header.

What to Expect for the Reviews

We aim to address all PRs in a timely manner. If no one reviews your PR within 5 days, please @-mention one of YuhanLiu11
, Shaoting-Feng or ApostaC.

[Shaoting-Feng]

LGTM