Set KubeOps.Generator as a DevelopmentDependency

[gamingrobot]

Fixes: #698
This will cause dotnet add package to add this to the PackageReference automatically:

<PrivateAssets>all</PrivateAssets>
<IncludeAssets>runtime; build; native; contentfiles; analyzers</IncludeAssets>

It will also show on nuget.org:

This flag is used by other source generators to fix the problem in #698

This flag is documented for .nuspec files but also works with dotnet pack in the csproj

[gamingrobot]

I think the build was broken from the .NET 9 action upgrades? https://github.com/buehler/dotnet-operator-sdk/actions/runs/12634004387/job/35200831312

[buehler]

Hi there :)

[buehler]

Thanks for your contribution!
And yes, I think the build is broken with the .net 9 setting of preview stuff. I try to have a look at it