Provide a configuration to configure total max event poolsize (cumulative count over horizontal scaling)

[soorajshankar]

Is your proposal related to a problem?

AFAIK the current the pool size configuration means `Max event processing threads` and this is per instance, and when Hasura runs horizontally this value could get multiplied.

What can go wrong?

• Suppose If I have a event stream that goes down for some time
• and when it comes back It could have significant load on the Hasura event queue
• I would expect Hasura to unload that without having more than 100 (or whatever the poolsize) request at the same time.
• Now if I have Hasura running horizontally (may be even with an auto scale setup) this could load my event handler in unexpectedly high rate.
• (If I have 3 hasura instances up, Hasura would have 300 simultaneous requests, which I may not expect my RHS system to handle)
• The event handler that I have in the RHS may not be designed to handle that much load, this could cause errors

Describe the solution you'd like

There should be a way to configure cumulative total max http poolsize instead of the event pool size. (just like total_max_connections)

Describe alternatives you've considered

If I have control over RHS, probably I can load balance RHS system or event increase the resources, but considering the expectation is to have Hasura manage the queue, this may not be a good solution.