feat: always include .env and .env.example

[c-ehrlich]

Closes #871

✅ Checklist

• I have followed every step in the contributing guide (updated 2022-10-06).
• The PR title follows the convention we established conventional-commit
• I performed a functional test on my final commit

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Changelog

• rename NEXT_PUBLIC_BAR to NEXT_PUBLIC_CLIENTVAR as it's more descriptive and we are already using this name in the docs anyway
• include a sample .env and .env.example file in all apps, even ones that don't need any env vars initially
• include schema files with those apps as well
• i'm leaning towards this feature but would be ok not merging if it's decided that we don't want this. the way i see it is that the downside is more files in a base app, and the upside is communicating more clearly our default env strategy.

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Screenshots

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🦋 Changeset detected

Latest commit: e816eed

The changes in this PR will be included in the next version bump.

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create-t3-app	Minor

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[juliusmarminge]

Don't think we need to add this new file, just make any necessary modifications here https://github.com/t3-oss/create-t3-app/blob/next/cli/template/base/src/env/schema.mjs

[github-actions]

⚡️ Lighthouse report for the changes in this PR:

Category	Score
🟠 Performance	79
🟢 Accessibility	100
🟢 Best practices	100
🟠 SEO	86
🟠 PWA	54

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