Since I see no replies yet, I'll give a sort of answer. I use Overseerr and my own self hosted domain name with Cloudns so that I can let my friends/family connect to it remotely to request stuff.
It sounds like it's definitely not 1:1 with what you're asking for since it only does sonarr and radarr and is not something accessible from messengers, but figured I'd mention it because it's been great for me. I use it for myself to add new stuff as well so I never have to go into the individual sonarr/radarr instances to add stuff.