Add draft-release composite action

[Yaswant Pradhan (yaswant)]

PR Summary

Add draft release composite action tailored for the Simulation Systems

Code Reviewer:

✅ Code Quality Checklist

(Some checks are automatically carried out via the CI pipeline)

• I have performed a self-review of my own code
• My code follows the project's style guidelines
• The modified workflow's README has been updated, if required
• The changes have been sufficiently tested (please describe)

🤖 AI Assistance and Attribution

• Some of the content of this change has been produced with the assistance of Generative AI tool name (e.g., Met Office GitHub Copilot Enterprise, GitHub Copilot Personal, ChatGPT GPT-4, etc) and I have followed the Simulation Systems AI policy (including attribution labels)

💻 Code Review

• The changes are appropriate and testing has been sufficient

[Copilot]

Pull request overview

Adds a reusable draft-release composite GitHub Action to generate categorised draft release notes (using a shared changelog template) and create/update a draft GitHub Release for the current tag.

Changes:

• Adds a composite action (draft-release/action.yaml) that checks out the caller repo, compiles release notes, and drafts/updates a GitHub Release.
• Adds a release-changelog category template (draft-release/templates/release.yml) plus documentation (draft-release/README.md).
• Updates Markdown lint configuration in pyproject.toml to allow Markdown constructs used by the new README.

Reviewed changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
pyproject.toml	Adjusts rumdl rule disables to accommodate new Markdown content.
draft-release/templates/release.yml	Defines changelog categories and excluded labels for release note generation.
draft-release/README.md	Documents the draft-release action, categories, usage, permissions, and outputs.
draft-release/bin/compile-release-notes.sh	Implements release note compilation from tags/commits and merged PR metadata.
draft-release/action.yaml	Defines the composite action steps to compile notes and create/edit draft releases.

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