Support for some host.json config at the function level

Today, settings like the queue visibility timeout is done at the host level, not the Function level, which means if I have two functions that need different settings, I have to use different Function Apps. It would be nice if I could over write the host.json settings with function specific settings, where possible.

From UserVoice: https://feedback.azure.com/forums/355860/suggestions/19103767

Start by reviewing how host.json settings, especially queue visibility timeout, are represented and applied. Determine which host-level settings can safely be overridden per function and define the expected function-specific configuration and precedence. Done means supported settings can differ between functions in the same Function App.

Written by the indexing model from the issue text.