[DOCS] Updates remote cluster and ccr docs#63517

Merged

gchaps merged 3 commits intoelastic:masterfrom gchaps:docs/remote-clusters-update

Apr 16, 2020

+100-52

Commits on Apr 14, 2020

[DOCS] Updates remote cluster and ccr docs
gchaps
committed

Commits on Apr 15, 2020

[DOCS] Adds section on managing clusters and follower indices
gchaps
committed

Commits on Apr 16, 2020

[DOCS] Incorporates review comments
gchaps
committed