[Feature request] auto configure DKIM key via libdns

[onny]

Use case

Since domain access to a domain provider might be already given with an api token for tls-dns challenge, why not support configuring DKIM key automatically using libdns?

• [x] I'm willing to help with the implementation

[foxcpp]

What is the benefit? For ACME it is automatic renewal - something that happens relatively frequently and is easily forgotten. DKIM keys are usually configured only once. Automatic DKIM key rotation might be a useful feature, though.

[onny]

Beside DKIM key rotation, also changing the DANE TLSA key manually after TLS key renew is painful :(