Provide arm (v7 32-bit) binaries for Raspberry Pi's

### Expected behavior

See `skaffold-linux-arm` in the release binary list, which is arm/v7 32-bit architecture (called `arm` in go)

### Actual behavior

I only see `skaffold-linux-arm64` in the release binary list, which is for arm/v8 64-bit architecture (called `arm64` in go)

### Information

Thanks so much for providing an arm64 binary in 2020. That can work in cloud arm/v8 servers (AWS Graviton, etc.) and in special Raspberry Pi 4's that have a custom kernel config.

However, Raspberry Pi 4's (by default), even though they have v8 64-bit support, don't yet come with 64-bit kernels in most configs (I think it's still considered a beta).

Also, most other Raspberry Pi's run arm/v7 aka arm 32-bit binaries. I often get students in my Kubernetes courses that ask how to develop on a Raspberry Pi, and I'd like them to be able to use skaffold on their Pi's. Many other K8s tools build for linux/arm/v7, and I'm hoping we can add skaffold to the list.