Rebase etcd base image from alpine to distroless

[wenjiaswe]

Rebasing etcd image to distroless/static make the image less vulnerable and avoid maintaining mutiple etcd images from the security (e.g. CVE), compatibility and build process concerns.

Xref: kubernetes is already in the process of rebasing images to distroless, see KEP for details: Rebase Kubernetes Main Master and Node Images to Distroless/static

/assign @wenjiaswe
/cc @yuwenma