Blazor node: B2C no longer available to new customers 5/1, supported until 2030

[guardrex]

[UPDATE] See the PR for final draft language.

cc: @danroth27 in case you have something you want to change about my plan for this issue, as this is a product/service offering type of update.

There are a few articles and a handful of B2C remarks around the Blazor node to address. I've worked out some coverage for this in the form of a NOTE that I may sprinkle around in the best spots. The note is going into the BWA Entra article now on #36367. The inline tracking remark "UPDATE 15.0" is to flag myself in 2030 (.NET 15) to remove the NOTE in articles that don't sunset (version out) in 2030.

Inline tracking note to self 🦖 ...

<!-- UPDATE 15.0 - Remove the following NOTE when .NET 15 releases in
                   2030, which is when B2C support will end for existing 
                   customers prior to 5/1/25. -->

Article NOTE ...

> [!NOTE]
> Azure Active Directory B2C is no longer available as a service to new customers as of May 1, 2025. AAD B2C tenants are supported for customers with accounts established prior to May 1, 2025 until 2030. For more information, see [Azure AD B2C: Frequently asked questions (FAQ)](/azure/active-directory-b2c/faq).