Logging sidecar refactoring

[crassirostris]

This is a replacement for https://github.com/kubernetes/contrib/tree/master/logging/fluentd-sidecar-gcp and https://github.com/kubernetes/contrib/tree/master/logging/fluentd-sidecar-es, describing general sidecar approach, including things not covered by docs above:

• Configuring sidecar logging agent using ConfigMaps
• Alternative use for sidecar, where it streams logs to stdout/stderr rather than has a logging agent inside

Related to #548

CC @piosz @devin-donnelly @steveperry-53

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[devin-donnelly]

@crassirostris , since release-1.5 has merged into Master, all changes should now target the Master branch. Please retarget this PR to master.

[janetkuo]

Thanks for this. I'm closing this PR just because GitHub doesn't allow updating target branch in a PR. Feel free to open a new one targeting master branch.