Dockerfile: stop using chainguard go image

Chainguard is no longer allowing free users to use specific versions of
images like go (instead, having to always use "latest"). So instead, we
will create our own build image by installing the needed packages on top
of the wolfi-base image.

This is one of the recommended approaches in their migration guide:
https://www.chainguard.dev/unchained/a-guide-on-how-to-use-chainguard-images-for-public-catalog-tier-users

Fixes #82

Signed-off-by: Will Norris <[email protected]>

Author: willnorris

Dockerfile

@@ -1,4 +1,5 @@
-FROM --platform=$BUILDPLATFORM cgr.dev/chainguard/go:1.20 as build
+FROM --platform=$BUILDPLATFORM cgr.dev/chainguard/wolfi-base as build
+RUN apk update && apk add build-base git openssh go-1.20
 
 WORKDIR /work