[FEAT] Add manual certificate option

[phedders]

Is this a new feature request?

• I have searched the existing issues

Wanted change

At the moment we have LE and zerossl - but many people manage their certs for multiple services. It would be great to have an option

CERTPROVIDER=none|manual

and let the cert mount their certs in /config/keys:ro

Reason for change

Many people manage their certs for multiple services, or use expensive certs etc...

Proposed code change

No response

[github-actions]

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