refactor(env-vars): data-seeder environment validation

[naftis]

#5932

Refactors data-seeder to use envalid and enforce setting environment variables in production.

[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]

Your environment is deployed to https://ocrvs-5932-data-seeder.opencrvs.dev.