scylla-gdb: Support new fair_{queue|group}s layout
scylla-gdb: Support new fair_{queue|group}s layout

In the recent seastar io_queues carry several fair_queues on board,
so do the io_groups. The queues are in boost small_vector, the groups
are in a vector of unique_ptrs. This patch adds this knowledge to
scylla-gdb script.

Signed-off-by: Pavel Emelyanov <c9a32589e048e044184536f7ac71ef92fe82df3e@scylladb.com>

scylladb/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla