feat(git): automatically add refs to commit

...messages

Add a `prepare-commit-msg` hook to automaically add `Refs` values, such
as issue IDs or commit SHAs to a Git commit message body by replacing an
`ISSUE_ID` placeholder that can be added to a commit message template.

templates/git-hooks/prepare-commit-msg.twig

@@ -0,0 +1,25 @@
+#!/usr/bin/env bash
+
+# {{ managedText }}
+
+set -euo pipefail
+
+# Load the issue ID from an `.issue-id` file within the project and replace the
+# `ISSUE_ID` placeholder within a Git commit message.
+#
+# For example, running `echo "OD-123" > .issue-id` will add `Refs: OD-123` to
+# the commit message.
+#
+# This also works with multiple issue IDs in the same string, e.g.
+# "OD-123 OD-456".
+
+PROJECT_DIR=$(git rev-parse --show-toplevel) # Get the root directory of the repo
+ISSUE_FILE="$PROJECT_DIR/.issue-id"
+
+if [ -f "${ISSUE_FILE}" ]; then
+  ISSUE_ID=$(cat "${ISSUE_FILE}" | sed 's/ /, /g')
+
+  if [ -n "${ISSUE_ID}" ]; then
+    sed -i.bak "s/# ISSUE_ID/Refs: $ISSUE_ID/" "$1"
+  fi
+fi