Remove `experimental.webapp.proxy.serviceType` config param from Installer

[mrsimonemms]

Is your feature request related to a problem? Please describe

In #11006, the experimental.webapp.proxy.serviceType parameter was deprecated. This should now be removed.

Describe the behaviour you'd like

Remove the deprecation notice from the config.go, the parameter from the experimental.go and where this is used in service.go

Describe alternatives you've considered

N/A

Additional context

The original suggestion was to remove this from the 2022.12.0 release. This may be moved as needs evolve