Add support to issue wildcard certificates

[leic4u]

There is a way to add the dns provider's information in DNS Credentials, and it's enough to issue a wildcard certificate.

Could you please support issuing wildcard certificates?

[leic4u]

I find the similar feature request in #100 , which allows panel users use custom commands to issue certificates.

If the feature that uses custom commands to issue certificates is supported, then the request in this issue can also be supported.

Waiting for it. Thanks to developers!