[feature request] Using sidecar type container for SidecarSet

[resouer]

What would you like to be added:

We may want to consider have https://github.com/kubernetes/enhancements/blob/master/keps/sig-apps/sidecarcontainers.md in plan as soon as it's ready.

Let's use this issue as tracker.

1. feature tracker: Sidecar Containers  kubernetes/enhancements#753
2. main kubelet change: Sidecar kubelet implementation kubernetes/kubernetes#80744

[furykerry]

sidecar type container in the kep doesn't align well with the one in sidecarset. sidecarset can operator *any" container in a pod, no matter it is a "sidecar", an "ambasador" or an "adaptor" per pod design pattern

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.