Build request: aarch64 image for `cockroach-self-signer-cert`

**Is your feature request related to a problem? Please describe.**
I was delighted to see `aarch64` images for CockroachDB and was indeed able to get it to deploy to my `arm64` k8s cluster via `Helm`. However, CockroachDB refuses to let me create DB users with passwords in insecure mode. While I believe that is a bit overprotective, I do actually like protecting even my internal traffic with TLS. Unfortunately, the self-signer image failed to run, as it was only built for `amd64`, thus leaving me with no sensible way to run CockroachDB.

**Describe the solution you'd like**
Add `aarch64` images for `cockroachlabs-helm-charts/cockroach-self-signer-cert`

**Describe alternatives you've considered**
There is a 3rd-party image for `cockroach-self-signer-cert` on Docker Hub, but it is not current, nor do I trust it. An official image is important.

Jira issue: CRDB-22875

Start by locating the build configuration for the cockroach-self-signer-cert image in this repository and checking how existing aarch64 CockroachDB images are produced. Confirm the image can run on an arm64 Kubernetes cluster through the Helm chart, and verify that an official aarch64 image is published.

Written by the indexing model from the issue text.