Add the Hashicorp repository to the pre-commit image.

Sometimes Terraform or Packer are needed. This will make it as all that
will be needed is an `apt-get update && apt-get install -y terraform`
without making the image bigger than it needs to be.

images/pre-commit/Dockerfile

 FROM buildpack-deps:bullseye
+COPY --chown=root:root sources.d/* /etc/apt/sources.list.d/
+SHELL ["/bin/ash", "-eo", "pipefail", "-c"]
 # hadolint ignore=DL3008,DL3013
-RUN apt-get update && \
+RUN curl -fsSL https://apt.releases.hashicorp.com/gpg | \
+    gpg --no-default-keyring --import --batch --keyring /usr/share/keyrings/hashicorp.gpg && \
+    apt-get update && \
     DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-recommends \
         docker.io \
         python3-dev \

images/pre-commit/sources.d/hashicorp.sources

+Types: deb
+URIs: https://apt.releases.hashicorp.com
+Suites: buster
+Components: main
+Signed-By: /usr/share/keyrings/hashicorp.gpg