ci: Build fixes

- Simplify builds by separating dev/stable workflows
- Fix Helm deploy key
- Remove deploy_key.env (already using deploy key in secrets)
- Fix paths matching on push and pull_request triggers
- Fix possible issues with tag difference between ERPNext and Frappe (add tag resolving step before pushing)
- Don't login, push Docker images and release Helm chart on forks
- Don't test on version 12 (there's no test for this version)
- Remove frappe-installer (from chore: use github actions #525)
- Fix badges in readme

README.md

@@ -1,6 +1,5 @@
-| Stable  | [![stable](https://github.com/frappe/frappe_docker/actions/workflows/docker.yml/badge.svg?event=repository_dispatch)](https://github.com/frappe/frappe_docker/actions/workflows/docker.yml)  |
-|---------|-----------------------------------------------------------------------------------------------------------------------------|
-| Nightly | [![nightly](https://github.com/frappe/frappe_docker/actions/workflows/docker.yml/badge.svg?event=schedule)](https://github.com/frappe/frappe_docker/actions/workflows/docker.yml) |
+[![Build Stable](https://github.com/frappe/frappe_docker/actions/workflows/build_stable.yml/badge.svg)](https://github.com/frappe/frappe_docker/actions/workflows/build_stable.yml) 
+[![Build Develop](https://github.com/frappe/frappe_docker/actions/workflows/build_develop.yml/badge.svg)](https://github.com/frappe/frappe_docker/actions/workflows/build_develop.yml)
 
 ## Getting Started