Users somewhat infrequently set a port mapping as the proxy type, causing issues in exposing apps publicly. Ideally we list out the available proxy types, but that would be a potential bc-break for non-core plugins, so this is the way to go for now.
Closes#6764
This change makes interacting with port mappings more clear - folks might previously set the port mapping to the proxy type or vice-versa.
The existing proxy:ports* commands still exist but will show a deprecation warning for a single minor release.
Moving verification of input to the earliest place is the best way to decrease the need to validate this further downstream.
Additionally, some of the existing checks were.... lacking :)
