Runtime: ConfigurationSource load async resource

[Meir017]

Problem:

I'm am trying to create a ConfigurationProvider that loads data from an http endpoint but there isn't a LoadAsync method to use.

Describe the solution you'd like

1. maybe add a virtual LoadAsync method to the ConfigurationProvider abstract class
2. add another type AsyncConfigurationProvider that only has a LoadAsync method and not the Load method
   

   Describe alternatives you've considered

using .GetAwaiter().GetResult() on the task

[guylando]

+1
By the way to preserve exceptions the better alternative (to .Result) is probably .GetAwaiter().GetResult() see: https://github.com/aspnet/Security/issues/59

[bdominguez]

+1

Even in Azure's repository you can see how to solve it incorrectly.

https://github.com/Azure/azure-sdk-for-net/blob/82432299d2705c4efc81c288067f1af9f0b1eb52/sdk/extensions/Azure.Extensions.Configuration.Secrets/src/AzureKeyVaultConfigurationProvider.cs#L53

[maryamariyan]

Next step for this is to prepare API suggestion and sample usage as per guideline in https://github.com/dotnet/runtime/blob/master/docs/project/api-review-process.md

[maryamariyan]

closing as dupe of https://github.com/dotnet/runtime/issues/36018