Acme dns provider support

[martcpp]

The ACME-DNS provider holds a single account (one server URL / username /password / subdomain). Because acme-dns keeps only the two most recent TXT values per record by design, every domain's _acme challenge CNAME points at the same acme-dns record, and only the last two written digests survive.

Acceptance criteria

• Per-domain credential selection implemented and config-driven.
• Backward compatible: existing single-account config works unchanged.
• wiremock tests cover per-domain selection and the 3-identifier case that currently fails.
• Docs updated to describe the map and remove the ≤2-identifier caveat once lifted.

[Hermann-Core]

Approved The ACME-DNS multi-domain support is correctly implemented: ✓ Per-domain credential selection works as specified ✓ Backward compatible: single-account config unchanged ✓ Two-value limit enforced at startup via check_order_domains() ✓ Comprehensive wiremock tests cover all scenarios ✓ Config validation catches misconfigurations at boot ✓ Domain normalization is consistent and correct ✓ Docs updated with clear examples The implementation handles all edge cases (conflicting accounts, empty fields, apex+wildcard sharing accounts) and surfaces configuration errors at startup rather than at renewal time. Tests pass, code is idiomatic.

[Hermann-Core]

@martcpp fix the conflicts on this branch and let's merge this ticket.

[martcpp]

@martcpp fix the conflicts on this branch and let's merge this ticket.

on it

[martcpp]

@ndefokou check this pr let merge thanks

[ndefokou]

Reviewed against issue #207. Implementation is solid and well-tested at the provider/config layer, but I have a few concerns — the main one being that the feature is effectively unreachable end-to-end because the ACME order is always for the single server.domain. Details inline.

[martcpp]

@ndefokou recheck

[ndefokou]

LGTM 🚀