extend installer to support choice of ingress type

[stefannica]

Currently, the FuseML installer has built-in support for Traefik and Istio as ingress solutions used for FuseML and built-in services. This support pertains to auto-detection and installation of an ingress solution (defaults to Istio). When it comes to extensions, this support is limited to reusing the same ingress solution used for FuseML. This has some major drawbacks:

• no support to install ingresses that are required by extensions in addition to the ingress used for FuseML. This is especially obvious with Traefik and KFServing. If Traefik is preinstalled, KFServing will not work, because it doesn't list Istio as a requirement. I'm not 100% sure, but the same might be valid for MLFlow.
• no support to select which ingress to use for FuseML and for each individual extension (in case of extensions where several ingress solutions are supported)

This is a proposal to improve the support for ingress services with FuseML built-in components and extensions. Some ideas of improvement:

• add an installer option to let users decide which ingress solution they want for FuseML core and built-in components
• add installer support for more ingress solutions, in addition to Traefik and Istio. This includes auto-detection as well as installation
• extend the installer extension DSL to support listing which ingress solutions are supported for an extension and list individual configuration changes (e.g. value.yaml overrides for helm charts) that are needed to install the extension configured for each ingress
• extend the installer to detect and automatically install (if missing) ingress services for extensions, based on what they list in their descriptors as supported ingress services