Since the removal of local discovery of #https://github.com/elastic/elasticsearch/pull/20960 we rely on minimum master nodes to be set in our test cluster. The settings is automatically managed by the cluster (by default) but current management doesn't work with concurrent single node async starting. On the other hand, with `MockZenPing` and the `discovery.initial_state_timeout` set to `0s` node starting and joining is very fast making async starting an unneeded complexity. Test that still need async starting could, in theory, still do so themselves via background threads.
Note that this change also removes the usage of `INITIAL_STATE_TIMEOUT_SETTINGS` as the starting of nodes is done concurrently (but building them is sequential)
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