[Doc]Restructure monitoring docs to support new and legacy internal collectors#11714

Merged

karenzone merged 6 commits intoelastic:masterfrom

karenzone:monitoring-take3

Apr 14, 2020

Commits on Feb 17, 2020

[Doc] added description of xpack.monitoring.collection.write_direct.enabled setting
andsel
committed
Added page to mark as deprecated the legacy internal collector and fixed all the `xpack.monitoring.*` references
andsel
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Commits on Feb 18, 2020

Included legacy collector file into monitoring overview
andsel
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Commits on Mar 23, 2020

Resolve conflicts
karenzone
committed

Commits on Apr 8, 2020

Restructure monitoring docs
karenzone
committed

Commits on Apr 14, 2020

Incorporate review comments
karenzone
committed