Enable ARM64 image

[kieran-ohara]

Is your feature request related to a problem? Please describe.
Hello, when I try to run this operator on a Kubernetes cluster using the ARM64 architecture there is an error that the ARM64 architecture is not supported. I may have to build the image myself and push it to my own repo but I would prefer to avoid that.

Describe the solution you'd like
I would like to be able the wordpress-operator on both x86 and ARM64 architectures

[calind]

In theory, you should be able to just add linux_arm64 to the root Makefile. The published docker images should be multi-arch, but you probably need to change the base image in images/wordpress-operator/Dockerfile.

If you manage to build arm64 images and want to become a maintainer for arm64 we're open to accepting pull requests for it.