Warn on MaximumReceiveMessageSize size (DOS risk)

[guardrex]

Per dotnet/aspnetcore#43974 (comment).

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Document Details

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• ID: 0969556b-b77e-bdb8-8e20-fd6971be0c25
• Version Independent ID: d17e4c28-ea82-0dd8-295d-19f6ada147ea
• Content: ASP.NET Core Blazor SignalR guidance
• Content Source: aspnetcore/blazor/fundamentals/signalr.md
• Product: aspnet-core
• Technology: aspnetcore-fundamentals
• GitHub Login: @guardrex
• Microsoft Alias: riande