[Resources]: Custom domains improvements

[jonaro00]

Custom domains is currently a Pro feature that requires some manual steps. https://docs.shuttle.rs/configuration/domain-names

This feature suggestion is to have an automatic way of setting up the SSL certificate, and automatic certificate renewal.

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_{This issue is a part of the Product Feature Poll (all issues). React with 👍 if you want this feature. Comment if you have suggestions related to this feature.}

[jonaro00]

Certificates for custom domains can now easily be added with a command on shuttle.dev: https://docs.shuttle.dev/docs/domain-names#set-up-ssl-certificate