**Backport:** https://codeberg.org/forgejo/forgejo/pulls/8550
- The `ACME_URL` setting is documented to default to Let's encrypt
production server if left empty, so do precisely that.
- Use a HTTP proxy to communicate with ACME if Forgejo is configured to
use that.
- Regression of forgejo/forgejo#7409 (previously certmagic took care of
setting these defaults).
- Resolvesforgejo/forgejo#8548
## Testing
1. Configure Forgejo's root URL to a public facing domain (that can pass a ACME challenge)
2. Configure Forgejo to use ACME by setting `[server].ENABLE_ACME = true` and `[server].ACME_ACCEPTTOS = true`.
3. Start Forgejo.
4. Observe that it's available via https.
Co-authored-by: Gusted <postmaster@gusted.xyz>
Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/8552
Reviewed-by: Earl Warren <earl-warren@noreply.codeberg.org>
Co-authored-by: forgejo-backport-action <forgejo-backport-action@noreply.codeberg.org>
Co-committed-by: forgejo-backport-action <forgejo-backport-action@noreply.codeberg.org>
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