REPO_POLICIES: move the example Dockerfiles into examples/

Each fenced dockerfile block moves byte for byte into its own file
under examples/, and one sentence links it where the block stood.
Phrases that pointed at a block by position now name the file. Both
checklists name the files. Rules keep their wording.

As #159 (comment) says.

Model: opus-5-5

examples/go-lint-system-libraries.Dockerfile

@@ -0,0 +1,8 @@
+FROM golangci/golangci-lint@sha256:... AS lint
+RUN apt-get update \
+    && apt-get install -y --no-install-recommends libvips-dev \
+    && rm -rf /var/lib/apt/lists/*
+WORKDIR /src
+COPY go.mod go.sum ./
+RUN go mod download
+ARG CACHEBUST