Fix stream keepalive on startup (#46640)

This was accidentally dropped in a previous PR that refactored the interaction
between stream and camera. This is difficult to test from the existing
preload stream tests, so leaving untested for now.

homeassistant/components/camera/__init__.py

@@ -258,6 +258,7 @@ async def async_setup(hass, config):
             stream = await camera.create_stream()
             if not stream:
                 continue
+            stream.keepalive = True
             stream.hls_output()
             stream.start()