Unifi: How to add TLS Certs?

Dear all

I was stupid enough to buy the UDM Pro and thus migrated from Self-Hosted away to Unifi OS.
Well, no Multi-Site, hiccups, container crashes. Enough is enough, so I’m back to square one with the Unifi addon.
Back in the days, I was able to add a TLS cert through the YAML config. Unfortunately this seems no longer possible. Does one of you have an idea how I could add the cert?