Usage of WEBSITE_USE_PLACEHOLDER_DOTNETISOLATED

#### Is your question related to a specific version? If so, please specify:
>.NET 8 isolate

#### What language does your question apply to? (e.g. C#, JavaScript, Java, All)
Either F# or C#

#### Question

In this [Guide for running C# Azure Functions in the isolated worker model](https://learn.microsoft.com/en-us/azure/azure-functions/dotnet-isolated-process-guide?tabs=windows#placeholders) it instructs to set the `WEBSITE_USE_PLACEHOLDER_DOTNETISOLATED` setting to `1` to improve cold starts, reading this it seems as though it should be applied to all `dotnet-isolated` function apps.

However, this [doc](https://learn.microsoft.com/en-us/azure/azure-functions/functions-app-settings#website_use_placeholder_dotnetisolated) implies that it is only applicable to apps running in a consumption plan.

Furthermore, #9588 suggest that this setting is not longer required.

So I guess I'm just seeking some clarification on if this setting is still relevant and how it should be used.
The less settings we are using will help our functions to be more maintainable in the future.

Thanks

Compare the .NET isolated process guide's placeholders section with the app settings documentation linked in the issue, then review the discussion in #9588. Determine whether WEBSITE_USE_PLACEHOLDER_DOTNETISOLATED remains relevant for .NET 8 isolated apps and which hosting plans it applies to. Done means the guidance is consistent and explicitly states when the setting should be used.

Written by the indexing model from the issue text.