Close connections asynchronously and improve gracefulness (dotnet#7006)

* Close connections asynchronously and improve gracefulness (dotnet#6762)

* Lock around connection cleanup so we don't call .Complete() and .CancelPendingFlush()/.CancelPendingRead() on the same pipe which results in an ObjectDisposedException

* Close connections asynchronously and improve gracefulness

Co-authored-by: ReubenBond <rebond@microsoft.com>

* Adding await for GatewayListNotification

* Updating GatewayManager interfaces

Co-authored-by: John Morman <jmorman@microsoft.com>
Co-authored-by: ReubenBond <rebond@microsoft.com>

Update NuGet.Config (dotnet#6873) (dotnet#6933)

Co-authored-by: Reuben Bond <203839+ReubenBond@users.noreply.github.com>

Add ADO.NET Provider support MySqlConector 0.x and 1.x. (dotnet#6831) (…

…dotnet#6860)

Co-authored-by: Han Liu <liuhan907@163.com>

Probe silos indirectly before submitting a vote (dotnet#6800) (dotnet…

…#6839)

* Probe silos indirectly before submitting a vote (dotnet#6800)

* Probe silos indirectly before submitting a vote

* Improve tests

* Remove no-longer necessary cases in SiloHealthMonitor, since concurrency has been removed.

* Changes for 3.4.0