added generic docker image for concourse tasks

.github/workflows/image_concourse-tools.yml

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+---
+name: "Image: concourse-tools"
+permissions:
+  actions: write # so 'cancel-workflow-action' can function
+
+on:
+  workflow_dispatch:
+  push:
+    branches:
+      - main
+  pull_request:
+    branches:
+      - main
+
+jobs:
+  workflows:
+    uses: ./.github/workflows/build-image-base.yml
+    with:
+      image: concourse-tools
+    secrets: inherit

concourse-tools/Dockerfile

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+FROM ghcr.io/alphagov/paas/bosh-cli-v2:main
+
+ENV AWSCLI_VERSION "1.19.112"
+
+RUN apt-get update && apt-get install -y \
+  curl \
+  python3 \
+  python3-pip \
+  && pip3 install \
+    awscli==$AWSCLI_VERSION

concourse-tools/README.md

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+# Concourse Tools
+
+This image is for building a container to run concourse tasks, which require various tools including: bosh-cli, awscli and curl. It uses bosh-cli-v2 as a base image and installs awscli on top using pip, and curl using apt.
+
+## Build locally
+
+```
+$ cd concourse-tools
+$ docker build -t concourse-tools .
+```
+
+## Run
+
+```
+docker run -it concourse-tools /bin/bash -c "bosh --version"
+```