Document support for async validation for Options

### Description

Document support for async validation for options once fully landed:

- https://github.com/dotnet/runtime/pull/128788
- https://github.com/dotnet/runtime/pull/129218
- https://github.com/dotnet/runtime/pull/130263

@ViveliDuCh @jeffhandley @halter73

### Page URL

https://learn.microsoft.com/en-us/aspnet/core/fundamentals/configuration/options?view=aspnetcore-11.0#options-validation

### Content source URL

https://github.com/dotnet/AspNetCore.Docs/blob/main/aspnetcore/fundamentals/configuration/options.md

### Document ID

dc7e3449-650b-d117-5eac-69e5ccb250cb

### Platform Id

c815d451-e2c8-0cf1-5862-03b12dd0392a

### Article author

@tdykstra

### Metadata

* ID: ed39cb0e-aa85-8bba-ffb4-859b56a60723
* PlatformId: c815d451-e2c8-0cf1-5862-03b12dd0392a
* Service: **aspnet-core**
* Sub-service: **fundamentals**

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