ci: Make builds release-channel aware. Add support for scheduled beta builds (#7323)

ADO-1121

---------

Co-authored-by: Jan Oberhauser <jan.oberhauser@gmail.com>

docker/images/n8n-custom/Dockerfile

@@ -1,4 +1,5 @@
 ARG NODE_VERSION=18
+ARG N8N_RELEASE_TYPE=dev
 
 # 1. Create an image to build n8n
 FROM n8nio/base:${NODE_VERSION} as builder
@@ -35,4 +36,5 @@ RUN \
 	chown node:node .n8n
 USER node
 ENV NODE_ENV=production
+ENV N8N_RELEASE_TYPE=${N8N_RELEASE_TYPE}
 ENTRYPOINT ["tini", "--", "/docker-entrypoint.sh"]

docker/images/n8n/Dockerfile

@@ -6,6 +6,7 @@ RUN if [ -z "$N8N_VERSION" ] ; then echo "The N8N_VERSION argument is missing!"
 
 ENV N8N_VERSION=${N8N_VERSION}
 ENV NODE_ENV=production
+ENV N8N_RELEASE_TYPE=stable
 RUN set -eux; \
 	apkArch="$(apk --print-arch)"; \
 	case "$apkArch" in \