[docker] add arm64 alpine*

hello, i'm trying to build an image with `alpine3.12` on following plateform [here](https://github.com/DrummyFloyd/crunchy-userinit-controller/pull/50)

- linux/amd64
- linux/arm64

it seems that at the moment , there is no `arm64` plateform

can you consider adding this plateform ?

thank you

```console
docker buildx build --platform linux/amd64,linux/arm64 . -t drummyfloyd/crunchy-userinit-controller:dev --no-cache
[+] Building 0.5s (3/3) FINISHED docker-container:multiarch
=> [internal] load build definition from Dockerfile 0.0s
=> => transferring dockerfile: 1.46kB 0.0s
=> CANCELED [linux/arm64 internal] load metadata for ghcr.io/astral-sh/uv:alpine3.12 0.4s
=> ERROR [linux/amd64 internal] load metadata for ghcr.io/astral-sh/uv:alpine3.12 0.4s
------
> [linux/amd64 internal] load metadata for ghcr.io/astral-sh/uv:alpine3.12:
------
WARNING: No output specified with docker-container driver. Build result will only remain in the build cache. To push result image into registry use --push or to load image into docker use --load
Dockerfile:2
--------------------
1 | # Use a Python image with uv pre-installed
2 | >>> FROM ghcr.io/astral-sh/uv:alpine3.12
3 |
4 | WORKDIR /app
--------------------
ERROR: failed to build: failed to solve: ghcr.io/astral-sh/uv:alpine3.12: failed to resolve source metadata for ghcr.io/astral-sh/uv:alpine3.12: ghcr.io/astral-sh/uv:alpine3.12: not found
```