ADNN Support

[sdpeters]

Enable gateway groups (ideally one gateway in each OSD node) to provide ADNN (a proposed NVMe feature) support to hosts. This will rely on ADNN support in SPDK. The Ceph specific work is to construct the hash hint parameters for each RBD image exposed as an NVMe namespace, and configure the SPDK targets in all the gateways to present the same hash hint parameters to their connected hosts. The hash hint parameters need to be regenerated and updated when the cluster map changes. See https://review.spdk.io/gerrit/c/spdk/spdk/+/4325/7/module/bdev/redirector/scripts/README for a rough idea of what's involved.

ADNN support requires gateway groups of arbitrary size.

We expect ADNN support to be developed concurrently with the standardization of ADNN, and probably not be an official NVMe-oF gateway feature until standardization is complete.

[Note: This feature should be mapped to the second gateway release]