chore: protect LTS release branches against force push and deletion

[Croway]

Summary

• Add camel-4.14.x and camel-4.18.x to protected_branches in .asf.yaml to prevent force pushes and accidental branch deletion
• Document the branch protection step in release-guide.adoc so future LTS branches are protected at creation time

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🧪 CI tested the following changed modules:

• docs

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