Add option to make Functions from Keda deployer externally available

Currently the Functions from the keda deployer (#3390) are only available cluster internally (no Ingress, ...). We should add an option to make them available externally as well e.g. via an Ingress/Gatewayroute/...

Start by tracing the Keda deployer and how its Functions are currently exposed only inside the cluster. Review the existing deployment and service configuration, then determine how an opt-in external exposure through an Ingress or GatewayRoute should be configured. Done means the option is documented and verified to expose the deployed Functions externally without changing the default internal-only behavior.

Written by the indexing model from the issue text.