[CHORE] Add GitHub issue templates for bug reports and feature requests

[stephrobert]

Is your feature request related to a problem? Please describe.

The project currently has no issue templates. Contributors must guess the expected format by reading existing issues. This leads to inconsistent issue quality and missing information (e.g., plumber version, reproduction steps, implementation hints).

Looking at the existing issues, a clear pattern has emerged organically:

• Feature requests follow: Problem → Solution → Implementation Hints → Files Touched → Why It's Valuable
• Bug reports need: Version, OS, steps to reproduce, expected vs actual behavior

Standardizing this with GitHub issue templates would improve issue quality and reduce back-and-forth.

Describe the solution you'd like

Add issue templates under .github/ISSUE_TEMPLATE/:

1. Feature Request (feature_request.yml)

A YAML form template with sections:

• Is your feature request related to a problem? (textarea, required)
• Describe the solution you'd like (textarea, required)
• Implementation Hints (textarea, optional — for contributors who've explored the codebase)
• Files Touched (textarea, optional)
• Why It's Valuable (textarea, optional)
• Describe alternatives you've considered (textarea, optional)

2. Bug Report (bug_report.yml)

A YAML form template with sections:

• Plumber version (plumber version output, required)
• Operating system (dropdown: Linux, macOS, Windows)
• GitLab version (input, optional — SaaS or self-managed version)
• Steps to reproduce (textarea, required)
• Expected behavior (textarea, required)
• Actual behavior (textarea, required)
• Relevant logs (textarea, optional — with hint to use --verbose)

3. Config template (config.yml)

Add a blank_issues_enabled: false option and links to:

• Discussions for questions
• Discord community
• CONTRIBUTING.md

Files to Create

• .github/ISSUE_TEMPLATE/feature_request.yml
• .github/ISSUE_TEMPLATE/bug_report.yml
• .github/ISSUE_TEMPLATE/config.yml

Why It's Valuable

Issue templates reduce friction for new contributors (they know exactly what information to provide), improve issue quality for maintainers (no missing context), and create a consistent look across all issues. This is a low-effort, high-impact improvement for the project's contributor experience.