Today, EDS attempts to open one stream per cluster to the management server when not being multiplexed over ADS. EDS streams support subscribing to more than one cluster, so this should not be necessary if the ApiConfigSource points to the same management server.

This is actually very noticeable when we have a large number of clusters. It shows up as stream resource exhaustion in H2 (#2941) as well as in internal performance benchmarks of configuration scalability.

The fix seems pretty easy, just need to do some level of aggregation similar to what ADS does.