we have compaction_manager.compactions metric for the number of active tasks,
but they don't account for tasks blocked waiting for an opportunity to run,
and they're the problematic ones.
Fixes#5254.
Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
Message-Id: <20200210131929.30981-1-raphaelsc@scylladb.com>