refactor: simple artifact example

To show/reproduce, check in tests & confirm fix for issue ##9830

Before:

```
$ ./skaffold build
Generating tags...
 - app -> localhost:32000/app:latest
 - base -> localhost:32000/base:f06ab6582db5b2f039bbfe557419b897c31a4161c69c6e7c7832f839b021a7e4
Some taggers failed. Rerun with -vdebug for errors.
Checking cache...
 - app: Not found. Building
 - base: Found Remotely
Starting build...

After:

```
$ ../../out/skaffold build
Generating tags...
 - app -> localhost:32000/app:6e10fde24150d5d16ab976db4d4f5a479522d3f82aa38606b7f15e1aef18be00
 - base -> localhost:32000/base:f06ab6582db5b2f039bbfe557419b897c31a4161c69c6e7c7832f839b021a7e4
Checking cache...
 - app: Found. Tagging
 - base: Found Remotely
```

Author: reingart

examples/simple-artifact-dependency/app/Dockerfile

@@ -1,15 +1,20 @@
 ARG BASE
-FROM golang:1.18 as builder
+
+FROM golang:1.18 AS builder
 WORKDIR /code
 COPY main.go .
 COPY go.mod .
 # `skaffold debug` sets SKAFFOLD_GO_GCFLAGS to disable compiler optimizations
 ARG SKAFFOLD_GO_GCFLAGS
 RUN go build -gcflags="${SKAFFOLD_GO_GCFLAGS}" -trimpath -o /app .
 
-FROM $BASE
+FROM $BASE AS base
+
+FROM scratch
 # Define GOTRACEBACK to mark this container as using the Go language runtime
 # for `skaffold debug` (https://skaffold.dev/docs/workflows/debug/).
 ENV GOTRACEBACK=single
 CMD ["./app"]
 COPY --from=builder /app .
+COPY --from=base hello.txt .
+

examples/simple-artifact-dependency/skaffold.yaml

@@ -9,6 +9,8 @@ build:
       alias: BASE
   - image: base
     context: base
+  tagPolicy:
+    inputDigest: {}
 manifests:
   rawYaml:
   - app/k8s-pod.yaml