Refactor certificate template filtering to avoid duplicate logic

[tareq89]

#10582
country pr: opencrvs/opencrvs-countryconfig#1067

Description

This PR improves the certificate template selector field configuration by fixing missing logic and enhancing the user experience.

Changes

• Fixed: defaultValue calculation now correctly respects template conditionals before selecting a default.
• Added: A noOptionsMessage to guide users when no templates are available for an event.
• Refactored: Certificate template filtering and default selection logic for better readability and maintainability.

Why

• Ensures that the default certificate is only applied when its conditionals are met.
• Provides clear feedback to users when no certificate templates are available, reducing confusion.
• Improves code clarity and reduces duplication.

Testing

• Verified that the default template is only preselected when its conditions are satisfied.
• Verified that the “No template available for this event, contact Admin” message is shown when no valid templates exist.
• Confirmed normal flows continue to work as expected.

Checklist

• I have linked the correct Github issue under "Development"
• I have tested the changes locally, and written appropriate tests
• I have tested beyond the happy path (e.g. edge cases, failure paths)
• I have updated the changelog with this change (if applicable)
• I have updated the GitHub issue status accordingly

[github-actions]

Oops! Looks like you forgot to update the changelog. When updating CHANGELOG.md, please consider the following:

• Changelog is read by country implementors who might not always be familiar with all technical details of OpenCRVS. Keep language high-level, user friendly and avoid technical references to internals.
• Answer "What's new?", "Why was the change made?" and "Why should I care?" for each change.
• If it's a breaking change, include a migration guide answering "What do I need to do to upgrade?".

[ocrvs-bot]

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