feat: allow custom frappe branch during asset image build

build/erpnext-nginx/install_app.sh

@@ -3,6 +3,7 @@
 APP_NAME=${1}
 APP_REPO=${2}
 APP_BRANCH=${3}
+FRAPPE_BRANCH=${4}
 
 [ "${APP_BRANCH}" ] && BRANCH="-b ${APP_BRANCH}"
 
@@ -12,7 +13,7 @@ echo -e "frappe\n${APP_NAME}" > /home/frappe/frappe-bench/sites/apps.txt
 
 mkdir -p apps
 cd apps
-git clone --depth 1 https://github.com/frappe/frappe ${BRANCH}
+git clone --depth 1 https://github.com/frappe/frappe -b ${FRAPPE_BRANCH}
 git clone --depth 1 ${APP_REPO} ${BRANCH} ${APP_NAME}
 
 echo "Install frappe NodeJS dependencies . . ."