Azure CLI updates for premium plan new settings

`az funcitonapp update` should be improved to surface a few new settings. One is a new setting that just completed deployment that lets you set the minimum function instance always running for an app. So maybe `az functionapp update --min-instances 10`. I don't see a setting for pre-warmed either which could also go in same spot `--pre-warmed-instances 1`

// @anthonychu

Start at the `az functionapp update` command and inspect how existing plan settings are exposed and sent to Azure. Confirm whether minimum and pre-warmed instance settings are supported by the relevant Azure API, then add coverage for both flags and verify their help text and update behavior.

Written by the indexing model from the issue text.