feat: add directline extensions support by default, for webapp runtime only

runtime/dotnet/azurewebapp/Microsoft.BotFramework.Composer.WebApp.csproj

@@ -2,6 +2,7 @@
 <Project Sdk="Microsoft.NET.Sdk.Web">
   <PropertyGroup>
     <TargetFramework>netcoreapp3.1</TargetFramework>
+    <AspNetCoreHostingModel>OutOfProcess</AspNetCoreHostingModel>
   </PropertyGroup>
   <ItemGroup>
     <None Include="ComposerDialogs\**">

runtime/dotnet/azurewebapp/Startup.cs

@@ -201,6 +201,7 @@ public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
         {
             app.UseDefaultFiles();
             app.UseStaticFiles();
+            app.UseNamedPipes(System.Environment.GetEnvironmentVariable("APPSETTING_WEBSITE_SITE_NAME") + ".directline");
             app.UseWebSockets();
             app.UseRouting()
                .UseEndpoints(endpoints =>