Add hadolint as Dockerfile linter (#20993)

* Added hadolint as Dockerfile linter in pipeline and resolved remaining hadolint issues in Dockerfile

* Use more specific version of hadolint Action

* Bumpt hadolint Action version to latest version to avoid deprecation notice

* Being _really_ specific now

.github/workflows/build-image.yml

@@ -18,6 +18,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v3
+      - uses: hadolint/hadolint-action@v3.0.0
       - uses: docker/setup-qemu-action@v2
       - uses: docker/setup-buildx-action@v2
       - uses: docker/login-action@v2

Dockerfile

@@ -15,7 +15,8 @@ SHELL ["/bin/bash", "-o", "pipefail", "-c"]
 WORKDIR /opt/mastodon
 COPY Gemfile* package.json yarn.lock /opt/mastodon/
 
-RUN apt update && \
+# hadolint ignore=DL3008
+RUN apt-get update && \
     apt-get install -y --no-install-recommends build-essential \
         ca-certificates \
         git \
@@ -50,10 +51,12 @@ SHELL ["/bin/bash", "-o", "pipefail", "-c"]
 ENV DEBIAN_FRONTEND="noninteractive" \
     PATH="${PATH}:/opt/ruby/bin:/opt/mastodon/bin"
 
+# Ignoreing these here since we don't want to pin any versions and the Debian image removes apt-get content after use
+# hadolint ignore=DL3008,DL3009
 RUN apt-get update && \
     echo "Etc/UTC" > /etc/localtime && \
     groupadd -g "${GID}" mastodon && \
-    useradd -u "$UID" -g "${GID}" -m -d /opt/mastodon mastodon && \
+    useradd -l -u "$UID" -g "${GID}" -m -d /opt/mastodon mastodon && \
     apt-get -y --no-install-recommends install whois \
         wget \
         procps \