Add clarity regarding whether the leading-dot notation in `NO_PROXY` matches only one subdomain or multiple

### Type of issue

Typo

### Description

In the description of `NO_PROXY`:

> Asterisks are not supported for wildcards; use a leading dot in case you want to match a subdomain. Examples: NO_PROXY=.example.com (with leading dot) will match www.example.com, but will not match example.com.

it is unclear whether `NO_PROXY=.example.com` will match multi-level subdomains e.g. `a.b.example.com` or only one subdomain, like the existing `www.example.com`.

Per https://github.com/dotnet/runtime/blob/d099f075e45d2aa6007a22b71b45a08758559f80/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpEnvironmentProxy.cs#L245, it appears that it _will_ match `a.b.example.com`.

Suggest additional clarification in the docs.

### Page URL

https://learn.microsoft.com/en-us/dotnet/api/system.net.http.httpclient.defaultproxy?view=net-10.0

### Content source URL

https://github.com/dotnet/dotnet-api-docs/blob/main/xml/System.Net.Http/HttpClient.xml

### Document Version Independent Id

54ed1a34-6d80-a38f-7d0e-cfd45ed18121

### Platform Id

9da6cfcc-942f-7b84-0c80-5b9f6b3e5842

### Article author

@karelz