Create custom-apps-podman

This is a full guide on building an image with custom apps using Podman.

docs/custom-apps-podman.md

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+## Prerequisites
+- podman
+- podman-compose
+- docker-compose
+
+Podman (the POD MANager) is a tool for managing containers and images, volumes mounted into those containers, and pods made from groups of containers. It is available on the official repositories of many Linux distributions. 
+
+## Step 1
+- Clone this repository and change the current directory to the downloaded folder
+  ```cmd
+    git clone https://github.com/frappe/frappe_docker
+    cd frappe_docker
+  ```
+## Step 2
+- Create `apps.json` file with custom apps listed in it
+  ```json
+    [
+     {
+       "url": "https://github.com/frappe/erpnext",
+       "branch": "version-15"
+     },
+   	  { 
+       "url": "https://github.com/frappe/hrms",
+       "branch": "version-15"
+     },
+     { 
+       "url": "https://github.com/frappe/helpdesk",
+       "branch": "main"
+     }
+   ]
+  ```
+  Check the syntax of the file using `jq empty apps.json`
+  ### Generate base64 string from JSON file:
+  `cmd export APPS_JSON_BASE64=$(base64 -w 0 apps.json)`
+
+## Step 3
+  - Building the custom image using podman
+ ```ruby
+   podman build \
+    --build-arg=FRAPPE_PATH=https://github.com/frappe/frappe \
+    --build-arg=FRAPPE_BRANCH=version-15 \
+    --build-arg=APPS_JSON_BASE64=$APPS_JSON_BASE64 \
+    --tag=custom:15 \
+    --file=images/layered/Containerfile .
+ ```
+   ### Note
+   - Make sure to use the same tag when you export a variable on the next step
+
+  ## Step 4
+  - Using the image
+  - Export environment variables with image name, tag and pull_policy
+    ```ruby
+        export CUSTOM_IMAGE=custom
+        export CUSTOM_TAG=15
+        export PULL_POLICY=never
+    ```
+  - Configuration of parameters used when starting the containers
+    - create `.env` file copying from example.env (Read more on setting up environemnt variables [here](https://github.com/frappe/frappe_docker/blob/main/docs/environment-variables.md)
+   
+ ## Final step
+ - Creating a compose file
+ - ```ruby
+    podman compose -f compose.yaml \
+   -f overrides/compose.mariadb.yaml \
+   -f overrides/compose.redis.yaml \
+   -f overrides/compose.noproxy.yaml \
+   config > ./docker-compose.yml
+   ```
+   ### NOTE
+   - podman compose is just a wrapper, it uses docker-compose if it is available or podman-compose if not. podman-compose have an issue reading .env files ([Issue](https://github.com/containers/podman-compose/issues/475)) and might create an issue when running the containers.  
+  - Creating pod and starting the containers
+      - `podman-compose --in-pod=1 --project-name erpnext -f ./docker-compose.yml up -d`
+
+## Creating sites and installing apps
+   - You can create sites from the backend container
+     - `podman exec -ti erpnext_backend_1 /bin/bash`
+       - `bench new-site myerp.net --mariadb-root-password 123456 --admin-password 123123`
+       - `bench --site myerp.net install-app erpnext`
+      
+## Troubleshoot
+- If there is a network issue while building the image, you need to remove caches and restart again
+  - `podman system reset`
+  - `sudo rm -rf ~/.local/share/containers/ /var/lib/container ~/.caches/containers`
+ 
+- Database issue when restarting the container
+  - Execute the following commands from **backend** container
+  - `mysql -uroot -padmin -hdb` (Note: put your db password in place of *admin*).
+  - `SELECT User, Host FROM mysql.user;` 
+  - Change the IP address to %, e.g. `RENAME USER '_5e5899d8398b5f7b'@'172.18.0.7' TO '_5e5899d8398b5f7b'@'%'`
+    
+