docs/zoned-storage: add zoned device documentation

docs/zoned-storage: add zoned device documentation

Add the documentation about the zoned device support to virtio-blk
emulation.

Signed-off-by: Sam Li <faithilikerun@gmail.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Reviewed-by: Dmitry Fomichev <dmitry.fomichev@wdc.com>
Acked-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 20230508045533.175575-9-faithilikerun@gmail.com
Message-id: 20230324090605.28361-9-faithilikerun@gmail.com
[Add index-api.rst to fix "zoned-storage.rst:document isn't included in
any toctree" error and fix pre-formatted code syntax.
--Stefan]
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>