Move "SignalR connection lifetime handling" section to the SignalR docs

[danroth27]

The section about Improved SignalR connection lifetime handling doesn't belong in this doc (my bad!) and should move to the SignalR docs.

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Document Details

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• ID: 542f38c-1502-f739-372a-80c86c377491
• Version Independent ID: 72c2a844-ffb2-4799-2c7a-a7a73d3b6833
• Content: Blazor hosting models
• Content Source: aspnetcore/blazor/hosting-models.md
• Product: aspnet-core
• Technology: aspnetcore-blazor
• GitHub Login: @guardrex
• Microsoft Alias: riande

[guardrex]

oops ... #12715

Beat you by 10 seconds. 🏃

I'll close that.

Cross-ref: dotnet/aspnetcore#9737 (comment)

[guardrex]

Looks like we only need to delete it in Blazor ...

https://docs.microsoft.com/aspnet/core/signalr/javascript-client?view=aspnetcore-3.0#automatically-reconnect