Artifact tests have been failing since the switch to the native nodetool, because ScyllaDB doesn't leave any IOCBs for tools. On some setups it will consume all of them and then nodetool and any other native app will refuse to start because it will fail to allocate IOCBs.
This PR fixes this by making use of the freshly introduced `--reserve-io-control-blocks` seastar option, to reserve IOCBs for tool applications. Since the `linux-aio` and `epoll` reactor backends require quite a bit of these, we enable the `io_uring` reactor backend and switch tools to use this backend instead. The `io_uring` reactor backend needs just 2 IOCBs to function, so the reserve of 10 IOCBs set up in this PR is good for running 5 tool applications in parallel, which should be more than enough.
Fixes: https://github.com/scylladb/scylladb/issues/19185
The problem this PR fixes has a manual workaround (and is rare to begin with), no backport needed.
Closesscylladb/scylladb#21527
* github.com:scylladb/scylladb:
main: configure a reserve IOCB for scylla-nodetool and friends
configure: enable the io_uring backend
main: use configure seastar defaults via app_template::seastar_options
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