add the ability to configure app-insights export

[bmc-msft]

Summary of the Pull Request

Adds the ability to enable automatic log export from the instance specific appinsights

PR Checklist

• Applies to work item: Enable auto-export from appinsights #44
• CLA signed. If not, go over here and sign the CLI.
• Tests added/passed
• Requires documentation to be updated
• I've discussed this with core contributors already. If not checked, I'm ready to accept this work might be rejected in favor of a different grand plan. Issue number where discussion took place: #xxx

Info on Pull Request

Adds the --export_appinsights to the deployment script to setup app insight exports to the app-insights container on the func storage account. Note, it will automatically replace any existing app-insights exports to the same container prior to creating the export config.

Validation Steps Performed

Deploy with --export_appinsights, run for a while. Note new files are created in app-insights container on func storage account.

[ranweiler]

Can we accomplish this with something other than an ad hoc (thus irrevocable) SAS URL?

[ranweiler]

Alternatively: use a much shorter-lived URL, and have a mechanism for refreshing within an instance (though that feels a bit roundabout).

[bmc-msft]

The API unfortunately requires SAS urls.

Doing it through the instance requires granting more privileges to the service.

[ranweiler]

Okay. Given the restrictions on perms, and the fact that none of our code touches it (it is only given directly to an Azure API, here), this seems okay to me. Can we just document our usage assumptions? In particular, note that this SAS URL must not "leave this script", except to the extent that it implicitly does in its use in the export request.