[DOCS] Adds overview and API ref for cluster voting configurations#36954

Merged

lcawl merged 7 commits intoelastic:masterfrom lcawl:voting

Jan 7, 2019

+263-149

Commits on Dec 22, 2018

Commits on Dec 31, 2018

Some suggested changes
DaveCTurner
committed

Commits on Jan 3, 2019