Add X-Accel-Buffering header to SSE responses (#1294) #2045

Job	Run time
build (ubuntu-latest, Debug)	6m 52s
build (ubuntu-latest, Release)	7m 9s
build (macos-latest, Release)	10m 14s
build (windows-latest, Release)	11m 19s
build (windows-latest, Debug)	11m 39s
build (macos-latest, Debug)	8m 6s
publish-coverage / publish-coverage	1m 2s
	56m 21s

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