tools: ynl: cli: Parse nested attributes in --list-attrs output

tools: ynl: cli: Parse nested attributes in --list-attrs output

Enhance the --list-attrs option to recursively display nested attributes
instead of just showing "nest" as the type.
Nested attributes now show their attribute set name and expand to
display their contents.

  # ./cli.py --family ethtool --list-attrs rss-get
  [..]
  Do request attributes:
    - header: nest -> header
        - dev-index: u32
        - dev-name: string
        - flags: u32 (enum: header-flags)
        - phy-index: u32
    - context: u32
  [..]

Reviewed-by: Nimrod Oren <noren@nvidia.com>
Signed-off-by: Gal Pressman <gal@nvidia.com>
Reviewed-by: Donald Hunter <donald.hunter@gmail.com>
Link: https://patch.msgid.link/20251118143208.2380814-3-gal@nvidia.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>