Modify func commands to handle nested app folder

[maiqbal11]

Follows from #1546 which would create a new folder structure for clearly separated unit tests. We will need additional work to detect and run from the nested function app folder rather than assuming that we are currently in the root where host.json is present.

[kulkarnisonia16]

This is a P1 for Python post GA - and one of the two big changes we are tracking for November.

[ahmedelnably]

Needs discussion, as this may involve a bigger restructuring of language handling