feat(playground): streaming chat completions (#4785) #9878

Job	Run time
Filter Changes	8s
Lint Phoenix	6m 46s
Test Phoenix (macos-12, 3.9)	11m 36s
integration-test (ubuntu-latest)	5m 39s
Tox	0s
Test Phoenix (windows-latest, 3.9)	10m 39s
integration-test (windows-latest)	3m 24s
Test Phoenix (ubuntu-latest, 3.9)	9m 20s
integration-test (windows-2019)	3m 38s
integration-test (macos-12)	5m 7s
	56m 17s

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