Disable seastar's built in handlers for SIGINT and SIGTERM and thus
fall-back to the OS's default handlers, which terminate the process.
This makes tool applications interruptable by SIGINT and SIGTERM.
The default handler just terminates the tool app immediately and
doesn't allow for cleanup, but this is fine: the tools have no important
data to save or any critical cleanup to do before exiting.
Fixes: scylladb/scylladb#16954Closesscylladb/scylladb#22838
aba4d07c62