Add New Custom Domains and Avoid Downtime while Let's Encrypt certificate Is Generated

Issue

When new custom domains are appended to to the existing list under "customDomains" in the "certs" part of the webserver LCP.json file, a new Let's Encrypt certificate is issued to include them. In the mean time the old domains will appear as having no current certificate.
Is it possible to add new custom domains to an existing Let's Encrypt certificate without temporarily affecting the certificate of the existing domains?

To avoid this temporary lack of certificate for the old domains, add the new domains in a separate customDomains block within the certs array of the LCP.json file. This will generate a new certificate for the new domains, while keeping the existing certificate for the existing domains active, preventing downtime.
```
"certs": [
  { "customDomains": ["existing.domain.com", "www.existing.domain.com"] },
  { "customDomains": ["new.domain.com", "www.new.domain.com"] }
]
```
This approach only applies to certificates generated by Let's Encrypt, not to custom certificates (Custom SSL) added via secret variables key and crt.