pack agenthost as tool (#5647)

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## Why are these changes needed?

convenience - allows to just run "agenthost"

```
dotnet pack --no-build --configuration Release --output './output/release' -bl\n
dotnet tool install --add-source ./output/release Microsoft.AutoGen.AgentHost
agenthost 
```

<!-- Please give a short summary of the change and the problem this
solves. -->

## Related issue number

<!-- For example: "Closes #1234" -->

closes #5646 

## Checks

- [ ] I've included any doc changes needed for
<https://microsoft.github.io/autogen/>. See
<https://github.com/microsoft/autogen/blob/main/CONTRIBUTING.md> to
build and test documentation locally.
- [ ] I've added tests (if relevant) corresponding to the changes
introduced in this PR.
- [ ] I've made sure all auto checks have passed.

docs/dotnet/core/index.md

@@ -89,6 +89,17 @@ using Microsoft.AutoGen.AgentHost;
 var autogenBackend = await Microsoft.AutoGen.RuntimeGateway.Grpc.Host.StartAsync(local: false, useGrpc: true).ConfigureAwait(false);
 ```
 
+You can also install the runtime as a dotnet tool:
+
+```
+dotnet pack --no-build --configuration Release --output './output/release' -bl\n
+dotnet tool install --add-source ./output/release Microsoft.AutoGen.AgentHost
+# run the tool
+# dotnet agenthost 
+# or just...  
+agenthost 
+```
+
 ### Running Multiple Agents and the Runtime in separate processes with .NET Aspire
 
 The [Hello.AppHost project](https://github.com/microsoft/autogen/blob/50d7587a4649504af3bb79ab928b2a3882a1a394/dotnet/samples/Hello/Hello.AppHost/Program.cs#L4) illustrates how to orchestrate a distributed system with multiple agents and the runtime in separate processes using .NET Aspire. It also points to a [python agent that illustrates how to run agents in different languages in the same distributed system](https://github.com/microsoft/autogen/blob/50d7587a4649504af3bb79ab928b2a3882a1a394/python/samples/core_xlang_hello_python_agent/README.md#L1).

dotnet/.config/dotnet-tools.json

@@ -6,13 +6,15 @@
       "version": "0.1.205",
       "commands": [
         "dotnet-repl"
-      ]
+      ],
+      "rollForward": true
     },
     "docfx": {
       "version": "2.67.5",
       "commands": [
         "docfx"
-      ]
+      ],
+      "rollForward": true
     }
   }
 }

dotnet/src/Microsoft.AutoGen/AgentHost/Microsoft.AutoGen.AgentHost.csproj

@@ -6,7 +6,16 @@
     <ContainerRepository>autogen-host</ContainerRepository>
     <ContainerFamily>alpine</ContainerFamily>
     <EnableSdkContainerSupport>true</EnableSdkContainerSupport>
-     </PropertyGroup>
+
+    <PackAsTool>true</PackAsTool>
+    <ToolCommandName>agenthost</ToolCommandName>
+    <PackageOutputPath>./nupkg</PackageOutputPath>
+  </PropertyGroup>
+
+
+
+  <Import Project="$(RepoRoot)/nuget/nuget-package.props" />
+
   <ItemGroup>
     <ContainerEnvironmentVariable Include="ASPNETCORE_HTTP_PORTS" Value="5001" />
     <ContainerPort Include="5001" Type="tcp" />