Added .NET 6 Target Framework

Author: michaelstaib

global.json

@@ -1,5 +1,5 @@
 {
     "sdk": {
-        "version": "5.0.103"
+        "version": "6.0.100-preview.7.21379.14"
     }
 }

src/Clients/src/Directory.Build.props

@@ -2,6 +2,6 @@
   <Import Project="$([MSBuild]::GetPathOfFileAbove('Directory.Build.props', '$(MSBuildThisFileDirectory)../'))" />
 
   <PropertyGroup>
-    <TargetFrameworks>net5.0; netcoreapp3.1</TargetFrameworks>
+    <TargetFrameworks>net6.0; net5.0; netcoreapp3.1</TargetFrameworks>
   </PropertyGroup>
 </Project>

src/Test.props

@@ -1,7 +1,7 @@
 <Project>
 
   <PropertyGroup>
-    <TargetFrameworks>net5.0;netcoreapp3.1</TargetFrameworks>
+    <TargetFrameworks>net6.0;net5.0;netcoreapp3.1</TargetFrameworks>
     <IsPackable>false</IsPackable>
   </PropertyGroup>