util/async-teardown: wire up query-command-line-options

Add new -run-with option with an async-teardown=on|off parameter. It is
visible in the output of query-command-line-options QMP command, so it
can be discovered and used by libvirt.

The option -async-teardown is now redundant, deprecate it.

Reported-by: Boris Fiuczynski <fiuczy@linux.ibm.com>
Fixes: c891c24b ("os-posix: asynchronous teardown for shutdown on Linux")
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Message-Id: <20230505120051.36605-2-imbrenda@linux.ibm.com>
[thuth: Add curly braces to fix error with GCC 8.5, fix bug in deprecated.rst]
Signed-off-by: Thomas Huth <thuth@redhat.com>