[SignalR][TS client] Send ping on connection start

[BrennanConroy]

Part of #23794

This changes the JS client to send a ping on connection startup instead of after ~15 seconds of inactivity. This helps the keep alive detection for when a client drops within the first few seconds of connecting. The .NET client already does this, so it's bringing the JS client up to par in this respect.

[halter73]

I am sad that we have to send a ping before the server starts requiring them. Can you link to the issue to properly handle this in the hub handshake?

Also, interesting to note. Doesn't this timeout anyone who has default server settings and then set a very large ping interval in the TS client? Could that be something someone has done? I hope not.

[BrennanConroy]

Can you link to the issue to properly handle this in the hub handshake?

#23794 is tracking that.

Doesn't this timeout anyone who has default server settings and then set a very large ping interval in the TS client? Could that be something someone has done? I hope not.

Yeah, that should be a very uncommon scenario. And if they are doing that, then in 7.0 they can fix it by setting the servers keep alive timeout to a large value.

[BrennanConroy]

@Pilchie for RC2. This is improving a scenario noticed by the Azure SignalR team where if a client disappears within the first ~15 seconds of connecting the server will take a long time to notice the client is gone.

[Pilchie]

Approved for .NET 7 RC2

[halter73]

Should we move #23794 out of rc2 and into .NET 8 planning then?

[BrennanConroy]

@dotnet/aspnet-admins please merge