Add NuGet metadata and package icon to project

Updated `DigitalData.MessagingService.Client.csproj`:
- Added NuGet metadata (PackageId, Authors, Company, etc.).
- Included `icon.png` as the package icon.
- Configured multi-targeting for `net462` and `net8.0`.
- Added XML documentation file generation.

Added `icon.png` binary file to the project.

src/DigitalData.MessagingService.Client/DigitalData.MessagingService.Client.csproj

@@ -2,10 +2,30 @@
 
   <PropertyGroup>
 	<TargetFrameworks>net462;net8.0</TargetFrameworks>
+	<DocumentationFile>bin\$(Configuration)\$(TargetFramework)\$(MSBuildProjectName).xml</DocumentationFile>
+	<PackageId>DigitalData.MessagingService.Client</PackageId>
+	<Authors>Digital Data GmbH</Authors>
+	<Company>Digital Data GmbH</Company>
+	<Product>DigitalData.MessagingService.Client</Product>
+	<Copyright>Copyright 2026</Copyright>
+	<PackageIcon>icon.png</PackageIcon>
+	<RepositoryUrl>http://git.dd:3000/AppStd/Rec.git</RepositoryUrl>
+	<PackageTags>digital data messaging service api client</PackageTags>
+	<Version>1.0.0-beta</Version>
+	<AssemblyVersion>1.0.0.0</AssemblyVersion>
+	<FileVersion>1.0.0.0</FileVersion>
+	<Description></Description>
   </PropertyGroup>
 	
   <ItemGroup>
     <PackageReference Include="RabbitMQ.Client" Version="7.2.1" />
   </ItemGroup>
 	
+  <ItemGroup>
+	<None Include="..\..\assets\icon.png">
+	<Pack>True</Pack>
+	<PackagePath>\</PackagePath>
+	</None>
+  </ItemGroup>
+	  
 </Project>