Add git_find_merged_branches script.

nix/configuration/roles/base/files/git_find_merged_branches.bash

@@ -0,0 +1,10 @@
+#!/usr/bin/env bash
+#
+# Find local branches that have been merged
+set -euo pipefail
+IFS=$'\n\t'
+DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
+
+: ${MAIN_BRANCH:="main"}
+
+git checkout -q ${MAIN_BRANCH} && git for-each-ref refs/heads/ "--format=%(refname:short)" | while read branch; do mergeBase=$(git merge-base ${MAIN_BRANCH} $branch) && [[ $(git cherry ${MAIN_BRANCH} $(git commit-tree $(git rev-parse "$branch^{tree}") -p $mergeBase -m _)) == "-"* ]] && echo "$branch"; done