Add article "How to install and configure Mercure on Hypernode"

docs/hypernode-platform/tools/how-to-install-and-configure-mercure.md

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+---
+myst:
+  html_meta:
+    description: Mercure is a real-time communication protocol that enables server-sent
+      events (SSE) for live updates in web applications. Learn how to install and
+      configure Mercure on your Hypernode.
+    title: How to install and configure Mercure on Hypernode?
+---
+
+# How to install and configure Mercure on Hypernode
+
+Mercure is a real-time communication protocol that enables server-sent events (SSE) for live updates in web applications. It's particularly useful for applications that need real-time notifications, live chat, or dynamic content updates.
+
+In this guide, we'll walk you through installing and configuring Mercure on your Hypernode using Supervisor to ensure it runs reliably as a background service. This may be required for Pimcore in the future.
+
+```{warning}
+Hypernode Support can't help or support this service on your Hypernode.
+```
+
+## Installing Mercure
+
+### Step 1: Download the Mercure binary
+
+First, navigate to the [Mercure releases page](https://github.com/dunglas/mercure/releases) and find the most recent legacy Linux x86_64 tar.gz file. For this example, we'll use version 0.20.2:
+
+```console
+app@abc-example-magweb-cmbl:~$ mkdir ~/mercure
+app@abc-example-magweb-cmbl:~$ cd ~/mercure
+app@abc-example-magweb-cmbl:~$ wget https://github.com/dunglas/mercure/releases/download/v0.20.2/mercure-legacy_Linux_x86_64.tar.gz
+app@abc-example-magweb-cmbl:~$ tar -xvzf mercure-legacy_Linux_x86_64.tar.gz
+app@abc-example-magweb-cmbl:~$ rm mercure-legacy_Linux_x86_64.tar.gz
+```
+
+This will extract the `mercure` binary to your `~/mercure` directory.
+
+### Step 2: Generate JWT keys
+
+Mercure uses JWT (JSON Web Tokens) for authorization. You'll need to generate a secret key for signing JWTs. You can generate a secure random key using:
+
+```console
+app@abc-example-magweb-cmbl:~$ openssl rand -base64 32
+```
+
+Save this key securely - you'll need it for both the Mercure server configuration and your application's JWT generation.
+
+## Configuring Mercure with Supervisor
+
+### Step 3: Create Supervisor configuration
+
+Create a Supervisor configuration file for Mercure. This ensures Mercure runs as a background service and automatically restarts if it crashes:
+
+```console
+app@abc-example-magweb-cmbl:~$ mkdir -p ~/supervisor
+app@abc-example-magweb-cmbl:~$ nano ~/supervisor/mercure.conf
+```
+
+Add the following configuration to the file:
+
+```ini
+[program:mercure]
+command=/data/web/mercure/mercure run -jwt-key=your-jwt-key --addr :8001
+directory=/data/web/mercure
+autostart=true
+autorestart=true
+stderr_logfile=/data/web/supervisor/mercure.err.log
+stdout_logfile=/data/web/supervisor/mercure.out.log
+user=app
+```
+
+**Important**: Replace `your-jwt-key` with the actual JWT secret key you generated in Step 2.
+
+### Step 4: Enable Supervisor (if not already enabled)
+
+If Supervisor isn't already enabled on your Hypernode, enable it:
+
+```console
+app@abc-example-magweb-cmbl:~$ hypernode-systemctl settings supervisor_enabled true
+app@abc-example-magweb-cmbl:~$ livelog
+```
+
+Wait for the changes to be applied before proceeding.
+
+### Step 5: Start Mercure
+
+Now reload Supervisor and start the Mercure service:
+
+```console
+app@abc-example-magweb-cmbl:~$ supervisorctl reread
+mercure: available
+app@abc-example-magweb-cmbl:~$ supervisorctl update
+mercure: added process group
+app@abc-example-magweb-cmbl:~$ supervisorctl start mercure
+```
+
+### Step 6: Verify Mercure is running
+
+Check that Mercure is running correctly:
+
+```console
+app@abc-example-magweb-cmbl:~$ supervisorctl status
+mercure                         RUNNING   pid 12345, uptime 0:00:05
+app@abc-example-magweb-cmbl:~$ curl http://localhost:8001/.well-known/mercure
+```
+
+If Mercure is working correctly, you should see a response indicating the Mercure hub is available.