introduce a basic format checker workflow using our dev image

.clang-format

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+---
+BasedOnStyle: Google

.github/format-check

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+#!/bin/bash
+#   formatting using the ldmx/dev image which has clang-format in it
+
+set -o errexit
+set -o nounset
+
+if [ -z "${GITHUB_WORKSPACE+x}" ]; then
+  # we are not in github actions so we need to error out
+  echo "ERROR: this script expects to be run in GitHub actions so should not be run locally."
+  exit 1
+fi
+
+ldmx() {
+  docker \
+    run \
+    --rm \
+    --volume ${GITHUB_WORKSPACE} \
+    --env LDMX_BASE=${GITHUB_WORKSPACE} \
+    ldmx/dev:latest \
+    ${PWD}
+    $@
+}
+find include/ -type f >  ${TMPDIR:-/tmp}/files-to-format.list
+find src/ -type f     >> ${TMPDIR:-/tmp}/files-to-format.list
+ldmx clang-format --verbose -Werror --dry-run $(cat ${TMPDIR:-/tmp}/files-to-format.list)

.github/workflows/format-check.yml

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+name: Check Format
+on:
+  push:
+    branches:
+      - 'trunk'
+  pull_request:
+
+jobs:
+  clang-format:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: run format check
+        run: ./.github/format-check