tools: ynl: cli: Add --list-attrs option to show operation attributes

tools: ynl: cli: Add --list-attrs option to show operation attributes

Add a --list-attrs option to the YNL CLI that displays information about
netlink operations, including request and reply attributes.
This eliminates the need to manually inspect YAML spec files to
determine the JSON structure required for operations, or understand the
structure of the reply.

Example usage:
  # ./cli.py --family netdev --list-attrs dev-get
  Operation: dev-get
  Get / dump information about a netdev.

  Do request attributes:
    - ifindex: u32
      netdev ifindex

  Do reply attributes:
    - ifindex: u32
      netdev ifindex
    - xdp-features: u64 (enum: xdp-act)
      Bitmask of enabled xdp-features.
    - xdp-zc-max-segs: u32
      max fragment count supported by ZC driver
    - xdp-rx-metadata-features: u64 (enum: xdp-rx-metadata)
      Bitmask of supported XDP receive metadata features. See Documentation/networking/xdp-rx-metadata.rst for more details.
    - xsk-features: u64 (enum: xsk-flags)
      Bitmask of enabled AF_XDP features.

  Dump reply attributes:
    - ifindex: u32
      netdev ifindex
    - xdp-features: u64 (enum: xdp-act)
      Bitmask of enabled xdp-features.
    - xdp-zc-max-segs: u32
      max fragment count supported by ZC driver
    - xdp-rx-metadata-features: u64 (enum: xdp-rx-metadata)
      Bitmask of supported XDP receive metadata features. See Documentation/networking/xdp-rx-metadata.rst for more details.
    - xsk-features: u64 (enum: xsk-flags)
      Bitmask of enabled AF_XDP features.

Reviewed-by: Nimrod Oren <noren@nvidia.com>
Signed-off-by: Gal Pressman <gal@nvidia.com>
Link: https://patch.msgid.link/20251118143208.2380814-2-gal@nvidia.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>