Fix certmagic usage. Fixes https://github.com/joohoi/acme-dns/issues/337

[maddes-b]

No separate certmagic cache needed. Default config and cache are sufficient to handle the certificates for the HTTP API. Updated to certmagic v0.20.

Issue of double cache was introduced by https://github.com/joohoi/acme-dns/commit/27e8251d11ba0a08c9b576fc04d61c1c7ba9b500 (from https://github.com/joohoi/acme-dns/pull/334), when updating certmagic to v0.17, and reported in https://github.com/joohoi/acme-dns/issues/337 Also maybe related to https://github.com/joohoi/acme-dns/issues/347, no cert, no update, no txt record.

Succesfully Tested (Ubuntu 22.04 LTS):

• normal renewal
• revoked cert renewal

Built on Ubuntu 22.04 LTS: GOPATH=/tmp/go-acme-dns CGO_ENABLED=1 go build (CGO_ENABLED for sqlite)

Installation on Ubuntu 22.04 LTS:

install -v -t /usr/local/bin/ acme-dns
install -v -d /etc/acme-dns/
install -v -t /etc/acme-dns/ config.cfg

adduser --system --gecos "acme-dns Service" --disabled-password --group --home /var/lib/acme-dns acme-dns
install -v -m u=rw-s,go=r-s -t /etc/systemd/system/ acme-dns.service
systemctl daemon-reload

systemctl enable acme-dns.service
systemctl start acme-dns.service

[maddes-b]

@joohoi This PR makes the current dev branch actually working again, Otherwise acme-dns fails to retrieve a certificate for its own API domain.