fix: update casing (#65)

### Description

Update the casing in the Dockerfile to resolve warnings

### Checklist
- [ ] Created tests which fail without the change (if possible)
- [ ] Extended the README / documentation, if necessary

packaging/docker/Dockerfile

@@ -1,5 +1,5 @@
 # For FIPS binary, there are some debian runtime dependencies
-FROM debian:12.5 as agent
+FROM debian:12.5 AS agent
 COPY observe-agent /
 # This shouldn't be necessary but sometimes we end up with execution bit not set.
 # ref: https://github.com/open-telemetry/opentelemetry-collector/issues/1317
@@ -12,13 +12,13 @@ RUN tar czhf observe-agent.tar.gz /observe-agent $(ldd /observe-agent | grep -oP
 # however, we can copy full directory as root (/) to be base file structure for scratch image
 RUN mkdir /output && tar xf /observe-agent.tar.gz --directory /output
 
-FROM alpine:3.20.2 as directories
+FROM alpine:3.20.2 AS directories
 RUN mkdir -p /var/lib/observe-agent/filestorage
 
-FROM alpine:3.20.2 as certs
+FROM alpine:3.20.2 AS certs
 RUN apk --update add ca-certificates
 
-FROM debian:12.5 as systemd
+FROM debian:12.5 AS systemd
 RUN apt update && apt install -y systemd
 # prepare package with journald and it's dependencies keeping original paths
 # h stands for dereference of symbolic links