fix(operator) close smoke test connection to scheduler

[lynnmatrix]

What this PR does / why we need it: Seldon v2 operator does not close smoke test connection to scheduler.

Moreover, the scheduler server sends the current model status in SubscribeModelStatus request handler and then observes close event. If the subscriber cancels the stream immediately after sending the subscription request, the scheduler will not receive the cancellation message and will not delete the stream. so the scheduler should send current model status asynchronously in goroutine.

Which issue(s) this PR fixes:

Special notes for your reviewer:

[seldondev]

Hi @lynnmatrix. Thanks for your PR.

I'm waiting for a SeldonIO or todo member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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