Better warnings when unable to determine function app language

Currently, it prints a warning multiple times when no functions worker runtime is specified at . @johnpapa can you please share a screenshot?

The warning should print once and should probably suggest a fix (create a local.settings.json). Perhaps we can instead prompt and ask what language and scaffold out the local settings file?

Start by reproducing the command-line case where no Functions worker runtime is specified and trace where the warning is emitted. Confirm the desired behavior with the issue discussion; done means the warning appears once and provides an actionable suggestion involving local.settings.json.

Written by the indexing model from the issue text.