Add predefined tags to project settings

[shainaraskas]

Summary

• Fixes [Website]: project tags can be custom or predefined #5035
• Added info about predefined tags where we talk about custom ones, so people don't recreate custom tags

More use cases will be documented for predefined tags as part of the CPS docs

Generative AI disclosure

1. Did you use a generative AI (GenAI) tool to assist in creating this contribution?

• Yes
• No

2. If you answered "Yes" to the previous question, please specify the tool(s) and model(s) used (e.g., Google Gemini, OpenAI ChatGPT-4, etc.).

Tool(s) and model(s) used: cursor auto

[github-actions]

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[github-actions]

🔍 Preview links for changed docs

• deploy-manage/deploy/elastic-cloud/project-settings.md

[yetanothertw]

LGTM, thank you! 🌻