feat(service): add PayloadCMS service template

[DragonBot00]

Changes

Added PayloadCMS service template with PostgreSQL 16. PayloadCMS is an open-source headless CMS built with Next.js and TypeScript.

Issues

• Fixes [Feature]: PayloadCMS Template #2346

Category

• Adding new one click service

AI Assistance

• AI was used (please describe below)

If AI was used:

• Tools used: Claude
• How extensively: Generated from PayloadCMS Docker docs, verified conventions

Testing

Verified YAML syntax and PostgreSQL health check pattern.

Contributor Agreement

Important

• I have read and understood the contributor guidelines. If I have failed to follow any guideline, I understand that this PR may be closed without review.
• I have searched existing issues and pull requests (including closed ones) to ensure this isn't a duplicate.
• I have tested all the changes thoroughly with a local development instance of Coolify and I am confident that they will work as expected when a maintainer tests them.