This PR tries to address the issue in 5199
where there were confusion on which image tag to use.
Because the image-specific `coredns/coredns-{arch}:version` is not usable
for all arch other than arm64, confusion happens.

This PR, for all arch-specific docker images:
1. Use `coredns/coredns:{arch}-version` (not `coredns/coredns-{arch}:version`)
   so that all images remain within the same docker repo (not multiple repos).
2. Push the arch-specific image `coredns/coredns:{arch}-version` to dockerhub.
3. Create manifest-specific `coredns/coredns:version` and `coredns/coredns:latest` from arch-specific images.
4. Push `coredns/coredns:version` and `coredns/coredns:latest` to dockerhub
5. Delete arch-specific image tags `coredns/coredns:{arch}-version` from dockerhub.

This will make arch-specific image tags invisible, but the  `coredns/coredns:version` and `coredns/coredns:latest`
will work as expected.
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>