File support for other secrets

What would you like to change?

There was a issue and pull request that add support for postgresql and auth secrets files, but I would like to ask if there could be file options for the rest:

GITHUB_*
SMTP_PASSWORD
TURNSTILE_SECRET_KEY
KANEO_TURNSTILE_SITE_KEY
SENTRY_API_TOKEN
CREEM_API_KEY
CREEM_WEBHOOK_SECRET
S3_ACCESS_KEY_ID
S3_SECRET_ACCESS_KEY

I'm mostly interested in SMTP and S3 since those were the ones I came across that weren't working when setting up.

Additional context

No response

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Originally requested by @Tim3Game on 2026-10-05. Original GitHub request #1937.