keys: Add partition_key::get_component() helper
keys: Add partition_key::get_component() helper

Signed-off-by: Pekka Enberg <add4fcd06328a394f0ad91feda7ee057316dc5ed@cloudius-systems.com>

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