Log error if `FUNCTIONS_WORKER_RUNTIME` missing and probing fails

When the host doesn't have `FUNCTIONS_WORKER_RUNTIME` set, it can fall back to probing behaviors for older worker models. However, the probing will not yield anything for newer models. The host is therefore unable to start a worker. It will default to using .NET in-process, and it will be unable to resolve function metadata. This leads to a hang state.

The host should be clear about the absence of the setting and what it is defaulting to. This is probably a series of warning and information logs, indicating the absence of `FUNCTIONS_WORKER_RUNTIME`, that the probing attempt for legacy models occurred, that the probing attempt didn't result in anything, and that it's defaulting to .NET in-process. This will help contextualize the fact that no functions are found in a later error.

In that series of logs, we should take opportunities to suggest that `FUNCTIONS_WORKER_RUNTIME` should be set for other stacks. We can also provide the values that would match for each available `workerConfig`.