Use UID and GID for USER in Dockerfile (#1922)

## Description

On clusters that strictly enforce no root containers via an Admission
Controller, they can't determine that a named user isn't 0 in the
container. This changes the container to identify the USER by UID and
GID so the admission controller can allow this through.

Chainguard documents the UID and GID of nonroot
https://edu.chainguard.dev/chainguard/chainguard-images/reference/static/overview/#users

## Related Issue

Fixes #1921

## Type of change

- [x] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Other (security config, docs update, etc)

## Checklist before merging

- [ ] Test, docs, adr added or updated as needed
- [ ] [Contributor Guide
Steps](https://github.com/defenseunicorns/zarf/blob/main/CONTRIBUTING.md#developer-workflow)
followed

---------

Co-authored-by: Wayne Starr <Racer159@users.noreply.github.com>

Dockerfile

@@ -1,8 +1,9 @@
 FROM cgr.dev/chainguard/static:latest
 ARG TARGETARCH
 
-USER nonroot:nonroot
+# 65532 is the UID of the `nonroot` user in chainguard/static.  See: https://edu.chainguard.dev/chainguard/chainguard-images/reference/static/overview/#users
+USER 65532:65532
 
-COPY --chown=nonroot:nonroot "build/zarf-linux-$TARGETARCH" /zarf
+COPY --chown=65532:65532 "build/zarf-linux-$TARGETARCH" /zarf
 
 CMD ["/zarf", "internal", "agent", "-l=trace", "--no-log-file"]