Upload 0.7.0-beta1 release to NuGet

[dbarbashov]

There is only 0.6.0-beta1 release available

[sergeyshaykhullin]

@eddynaka Please, update and upload to NuGet contrib packages to latest version, for now we can't use them with 1.0.0 rc at all
Lately we had workarounds, warnings but all is worked =(

  Startup.cs(126, 6): [CS7069] Reference to type 'TracerProviderBuilder' claims it is defined in 'OpenTelemetry', but it could not be found

[eddynaka]

@sergeyshaykhullin , we are still checking how we will do that, since a lot of stuff changed and became internal.

I will try to update ASAP.

[eddynaka]

@sergeyshaykhullin , I tried the migration but that isn't easy since the prs that changed many classes to internal. We will have to wait some news from the main repo to migrate...

For now, this is a duplicate from #49, so I will close this for now. And, we will have to wait for this: open-telemetry/opentelemetry-dotnet#1580