Update to Azure.Identity 1.8.0 dependency

Hello,

Maybe you already have this in mind but App Insights relies on Azure.Identity to get bearer token in case you want to use AAD authentication to send metrics to App Insights. The problem is that before version 1.8.0 of Az.Identity the ManagedIdentityCredential was not doing any token cache, neither App Insights do (there is a dicussion for this here: https://github.com/microsoft/ApplicationInsights-dotnet/issues/2539#issuecomment-1341300967), which results in a lot of token generation roundtrip with performance degradation. On Azure functions the version used for Az.Identity is 1.5.0, so could you plan to rollout the Az.Identity file version in the Azure funtions to 1.8.0 or maybe is there a way to update it manually?

Regards.