[Feature]: When created certificates, show them as a dropdown when adding domains

What problem will this feature address?

When i create a domain for a service and i want to create my own custom certificate for it, i need to write down the exact title of that certificate which is error sensitive

Describe the solution you'd like

When you add a domain for a service and you select custom, it would be nice to have the field as a dropdown, the dropdown shows you the options of the ssl certificates you've entered on the "certificates" page. that way you cannot misspell the certificates.

you can add a additional checkbox for people who want to use something real custom and that is not read from the certificates page. see here an example:

Describe alternatives you've considered

n/a

Additional context

No response

Will you send a PR to implement it?

No

Start by locating the form for adding a service domain and the certificates page in the repository, then trace how certificate names are loaded and selected. Confirm how the existing custom certificate field is represented before choosing the dropdown behavior. Done means available certificates can be selected without misspelling while an explicitly enabled custom option remains possible.