UUF: File-uploads.md: broken link: how to download a sample

[wadepickett]

Description

Fix broken "how to download a sample" link in file-uploads.md

User feedback transferred from UUF System:

"this https://learn.microsoft.com/en-us/aspnet/core/mvc/models/file-uploads?view=aspnetcore-9.0 page has a "how to download" link that points to https://learn.microsoft.com/en-us/aspnet/core/overview?view=aspnetcore-9.0#how-to-download-a-sample but this segment does not exist now"

Problem:
The "how to download a sample" link in the file-uploads.md article is broken. The section exists in the fundamentals/index.md file, but the automatically generated anchor ID in the published HTML doesn't match the expected format in the cross-reference.

When users click on the link to download the sample code, they're redirected to a page that doesn't scroll to the "How to download a sample" section, making it appear as if the section doesn't exist.

Solution:
Add an explicit anchor ID to the "How to download a sample" heading in the fundamentals/index.md file to ensure that cross-references to this section work correctly.

Implementation details:

1. Locate the "How to download a sample" heading in fundamentals/index.md (around line 239)
2. Add an explicit anchor ID to ensure the link works as expected

Current:

## How to download a sample

### Page URL

https://learn.microsoft.com/en-us/aspnet/core/mvc/models/file-uploads?view=aspnetcore-9.0

### Content source URL

https://github.com/dotnet/AspNetCore.Docs/blob/main/aspnetcore/mvc/models/file-uploads.md

### Document ID

c6787f0f-3e9a-6efb-0e6e-5ccb957d3f4a

### Platform Id

a281e7a8-71e2-c3ec-e6dc-c5c6161ae486

### Article author

@tdykstra

### Metadata

* ID: 9a5cfa38-0e6c-4346-dafc-84ea5c513fcf
* PlatformId: a281e7a8-71e2-c3ec-e6dc-c5c6161ae486 
* Service: **aspnet-core**
* Sub-service: **mvc**

[Related Issues](https://github.com/dotnet/AspNetCore.Docs/issues?q=is%3Aissue+is%3Aopen+c6787f0f-3e9a-6efb-0e6e-5ccb957d3f4a)

[guardrex]

@wadepickett ... You must have not seen the earlier ping yet ... #36054 (comment) ... these were all fixed on #36016.