Support rate limit = -1 to disable rate limit or some other session var

[kwannoel]

Currently, the behaviour of rate limit 0 is used for this purpose. But its behaviour is not entirely consistent, for example, when setting it locally in the with options, it will apply rate limit, and stall the entire stream (cr @tabVersion ).

To fix that, we need to support another way of disabling rate limit. And then make sure rate limit = 0 is setup in a way which doesn't block streams.