In a lambda returned from make_streaming_consumer() there's a check for
current scheudling group being streaming one. It came from #17090 where
streaming code was launched in wrong sched group thus affecting user
groups in a bad way.
The check is nice and useful, but it abuses replica::database by getting
unrelated information from it.
To preserve the check and to stop using database as provider of configs,
keep the streaming scheduling group handle in the debug namespace. This
emphasises that this global variable is purely for debugging purposes.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
Closesscylladb/scylladb#28410