No language selection for nested Function Apps

1. func init (Select a language L)
2. mkdir nestedApp
3. cd nestedApp
4. func init (func assumes the language to be L)

We should maybe throw an error for nested Function Apps or at the least not assume a worker runtime.

This should be a low-pri item as this isn't a blocking scenario and ideally users shouldn't be hitting this case.

cc: @ColbyTresness

Reproduce the sequence with `func init`, a nested `nestedApp` directory, and a second `func init` to confirm how the language is selected. Start at the `func init` command entry point and determine whether the completed behavior should reject nested Function Apps or avoid assuming the parent worker runtime; done when that behavior is explicit and covered by a regression test.

Written by the indexing model from the issue text.