minor #11084 Real-time capabilities: add docs for the Mercure Component and Bundle (dunglas)

This PR was merged into the 4.2 branch.

Discussion
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Real-time capabilities: add docs for the Mercure Component and Bundle

Docs for https://github.com/symfony/mercure-bundle and https://github.com/symfony/mercure.

Commits
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9c31073 Real-time capabilities: add docs for the Mercure integration

Author: javiereguiluz

_images/mercure/chrome.png

@@ -0,0 +1,48 @@
+.. index::
+   single: Mercure
+   single: Components; Mercure
+
+The Mercure Component
+=====================
+
+    `Mercure`_ is an open protocol allowing to push data updates to web
+    browsers and other HTTP clients in a convenient, fast, reliable
+    and battery-friendly way.
+    It is especially useful to publish real-time updates of resources served
+    through web APIs, to reactive web and mobile apps.
+
+The Mercure Component implements the "publisher" part of the Mercure Protocol.
+
+Installation
+------------
+
+.. code-block:: terminal
+
+    $ composer require symfony/mercure
+
+Alternatively, you can clone the `<https://github.com/symfony/mercure>`_ repository.
+
+.. include:: /components/require_autoload.rst.inc
+
+Usage
+-----
+
+The following example shows the component in action::
+
+    // change these values accordingly to your hub installation
+    define('HUB_URL', 'https://demo.mercure.rocks/hub');
+    define('JWT', 'eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJtZXJjdXJlIjp7InN1YnNjcmliZSI6WyJmb28iLCJiYXIiXSwicHVibGlzaCI6WyJmb28iXX19.LRLvirgONK13JgacQ_VbcjySbVhkSmHy3IznH3tA9PM');
+
+    use Symfony\Component\Mercure\Publisher;
+    use Symfony\Component\Mercure\Update;
+    use Symfony\Component\Mercure\Jwt\StaticJwtProvide;
+
+    $publisher = new Publisher(HUB_URL, new StaticJwtProvide(JWT));
+    // Serialize the update, and dispatch it to the hub, that will broadcast it to the clients
+    $id = $publisher(new Update('https://example.com/books/1.jsonld', 'Hi from Symfony!', ['target1', 'target2']));
+
+Read the full :doc:`Mercure integration documentation </mercure>` to learn
+about all the features of this component and its integration with the Symfony
+framework.
+
+.. _`Mercure`: https://mercure.rocks

_images/mercure/discovery.png

@@ -41,6 +41,7 @@ Topics
     frontend
     http_cache
     logging
+    mercure
     messenger
     performance
     profiler