Mark csharp template as deprecated

In favour of dotnet8-csharp

Signed-off-by: Alex Ellis (OpenFaaS Ltd) <[email protected]>

template/csharp/template.yml

@@ -1,11 +1,7 @@
 language: csharp
 fprocess: dotnet ./root.dll
 welcome_message: |
-  You have created a C# function using the Classic OpenFaaS Template.
+  This template is deprecated and will be removed in a future
+  release.
 
-  To include third-party dependencies edit your .csproj file or install
-  Nuget packages with VSCode.
-
-  For high-throughput applications, we recommend using the csharp-kestrel
-  or csharp-httprequest templates available in the OpenFaaS template
-  store.
+  Use dotnet8-csharp instead.