Add roadmap to assembler.yml

[lcawl]

This PR adds https://github.com/elastic/roadmap to the config/assembler.yml so that it won't generate warnings when it's used in issue links in changelogs.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 0c2f2c0 and fcf960b.

📒 Files selected for processing (1)

• config/assembler.yml

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📝 Walkthrough

Walkthrough

The pull request adds a new repository reference configuration entry to config/assembler.yml. The roadmap reference is configured with private: false (publicly accessible) and skip: true (to be skipped during processing). This represents the addition of a previously unconfigured repository reference with explicit privacy settings and processing behavior.

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title 'Add roadmap to assembler.yml' directly and clearly describes the main change in the pull request.
Description check	✅ Passed	The description explains the purpose of adding the roadmap repository to config/assembler.yml to prevent warnings in changelog issue links.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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✨ Finishing Touches

✨ Simplify code

• Create PR with simplified code
• Commit simplified code in branch roadmap-repo

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