Support refresh of App Config references in Azure App Services

[avanigupta]

Enable automatic refresh of AppConfig references in AppService. Currently, the only way to see updates to referenced values is by restarting App Service application. Like KeyVault references, AppService platform could offer 24 hour auto-refresh for AppConfig references too, ensuring that changes are reflected without requiring a restart.

Based on customer feedback:

@zhenlan Bouncing Yes, automatically restarting - even ~24hrs after changing config - would be useful when changing non-essential config, like log level or APM config.

Originally posted by @carlo-quinonez in #62