HTTP/3: Support request body rate timeout

[JamesNK]

• Respect configuration
• Add unit tests
• Ensure it can be disabled with feature

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[halter73]

Edit: Since this is a bit much for what started as a limited issue I've opened #29702 with all the items below.

I think we should have equivalents to most of Http2TimeoutTests for HTTP/3.

More timeouts to add and/or verify:

• Min combined response rate timeouts
  • KestrelServerLimits.MinResponseDataRate
  • This is everything sent to the client. The response headers, response body, control frames, etc...
• Response drain timeouts
  • Derived from KestrelServerLimits.MinResponseDataRate and KestrelServerLimits.MaxResponseBufferSize
  • When there's backpressure on the underlying stream/connection after PipeWriter.FlushAsync() completes which can happen with non-zero PauseWriterThreshold.
• Request header timeouts
  • KestrelServerLimits.RequestHeadersTimeout
• Keep-alive timeouts
  • KestrelServerLimits.KeepAliveTimeout
  • We probably don't want to keep idle QuicConnections around forever

If any the above bullet points aren't implemented yet, they probably deserve their own issue. The same goes for the size and count based limits in KestrelServerLimits.

• MaxRequestLineSize
• MaxRequestHeadersTotalSize
• MaxRequestHeaderCount
• MaxRequestBodySize
• MaxConcurrentConnections