Make appsettings.json easier for users to update
Make appsettings.json easier for users to update

by changing from two variables they have to replace to just one.

Change-Id: I8895f50c88106220c5346bc68725068f00f448cf

GoogleCloudPlatform/getting-started-dotnet,GoogleCloudPlatform/getting-started-dotnet,GoogleCloudPlatform/getting-started-dotnet