CP-44752: SDK(C#): add .Net 8.0 as target

Apparently this has fewer dependencies than netstandard2.0,
and some projects would've picked net45 in favour of netstandard2.0.

Eventually we may want to drop net45, for now just add the new target.

There is also net9.0, but it has an EOL date ahead of net8.0 which is LTS.

A quick sanity test that the net80 target includes tracing support:
```
make sdksanity
strings -el ./_build/default/ocaml/sdk-gen/csharp/autogen-out/src/bin/Release/net80/XenServer.dll|grep traceparent                                             traceparent
```

Signed-off-by: Edwin Török <[email protected]>

Author: edwintorok

ocaml/sdk-gen/csharp/autogen/src/XenServer.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <Version>0.0.0</Version>
-    <TargetFrameworks>netstandard2.0;net45</TargetFrameworks>
+    <TargetFrameworks>net80;netstandard2.0;net45</TargetFrameworks>
     <OutputType>Library</OutputType>
     <RootNamespace>XenAPI</RootNamespace>
     <GenerateAssemblyInfo>True</GenerateAssemblyInfo>