Cherry-pick to 7.9: docs: Restructure and deduplicate security docs (#18594)#20070

Merged

bmorelli25 merged 1 commit intoelastic:7.9from bmorelli25:backport/7.9/pr-18594

Jul 21, 2020

+206-203

Commits on Jul 20, 2020

docs: Restructure and deduplicate security docs (elastic#18594 )
bmorelli25
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