Extension - Add support for RouterChannel request refreshing

[huntharo]

Motivations

• In unlikely scenarios, the extension could get stuck open until there is a request sent from the router on each open channel, allowing the subsequent re-request to get a 409
• These scenarios, while infrequent, could be very costly

Acceptance Criteria

• Add support to the Extension for a status code that indicates "call me again"
  • This could be 204 No Content which would trigger the next request loop
  • Do not send this status code from the router until supported by the extension
  • When there are other users, this sort of change would need to have the Extension identify that it supports a particular feature when it connects - This can be done by setting a features header on the router channel request
• Consider support to the Router for a 103 Early Hint with a Lambda-Dispatch-Control header that can ask for closing
• Consider extracting the /api/chunked/close request into a location where it can be independently invoked on errors
  • This should attempt to establish a new connection for the request
  • If the connection fails, the channels should exit after:
    • A lengthy (20-30 seconds) timeout if there are requests in flight, unless the count drops to zero
    • A short (5 seconds) timeout if there are no requests in flight and no requests arrive during that timeout