[Bug] Application startup tasks can block the Vertx event loop

[andrewazores]

          Vertx's default setting is to have `cpuCores * 2` threads in the pool, so definitely adding a bunch of extra threads here like this is going to increase the size of the pool substantially for most deployments. The proper fix would be to avoid doing blocking work on startup, or at least move that blocking work off of a Vertx event loop thread, but that's a relatively deep change and I haven't had enough time to look into it yet. If I have time before the next 2.4 release I will, but it seems riskier to do that than to simply bump up the minimum pool size a bit for now.

Originally posted by @andrewazores in https://github.com/cryostatio/cryostat/pull/1650#discussion_r1318986255