sstables: add method to get compaction metadata
sstables: add method to get compaction metadata

Signed-off-by: Raphael S. Carvalho <1e2942cea40e3b4d2162dfcd9e53e41c05a84d22@cloudius-systems.com>

eklitzke/scylla,tempbottle/scylla,capturePointer/scylla,linearregression/scylla,kjniemi/scylla,kangkot/scylla,eklitzke/scylla,wildinto/scylla,bowlofstew/scylla,respu/scylla,senseb/scylla,stamhe/scylla,glommer/scylla,victorbriz/scylla,phonkee/scylla,bowlofstew/scylla,scylladb/scylla,kjniemi/scylla,raphaelsc/scylla,aruanruan/scylla,duarten/scylla,senseb/scylla,wildinto/scylla,eklitzke/scylla,rentongzhang/scylla,justintung/scylla,phonkee/scylla,kjniemi/scylla,aruanruan/scylla,stamhe/scylla,linearregression/scylla,scylladb/scylla,rentongzhang/scylla,asias/scylla,raphaelsc/scylla,bowlofstew/scylla,scylladb/scylla,kangkot/scylla,guiquanz/scylla,dwdm/scylla,dwdm/scylla,shaunstanislaus/scylla,avikivity/scylla,asias/scylla,aruanruan/scylla,rluta/scylla,raphaelsc/scylla,tempbottle/scylla,phonkee/scylla,duarten/scylla,justintung/scylla,kangkot/scylla,justintung/scylla,acbellini/scylla,tempbottle/scylla,gwicke/scylla,acbellini/scylla,gwicke/scylla,shaunstanislaus/scylla,linearregression/scylla,rluta/scylla,avikivity/scylla,victorbriz/scylla,wildinto/scylla,gwicke/scylla,scylladb/scylla,glommer/scylla,capturePointer/scylla,acbellini/scylla,respu/scylla,senseb/scylla,rentongzhang/scylla,victorbriz/scylla,rluta/scylla,guiquanz/scylla,respu/scylla,avikivity/scylla,asias/scylla,guiquanz/scylla,shaunstanislaus/scylla,duarten/scylla,capturePointer/scylla,glommer/scylla,dwdm/scylla,stamhe/scylla