Pull Request for Issue #36898.

This is a reopened version of PR #44894. I can't reopen the #44894 for technical reasons, sorry 😱

Summary of Changes

This PR adds an ability to configure Joomla using environment variables. To do this, the config provider has been changed to load all environment variables whose names start with JOOMLA_ (e.g. JOOMLA_DEBUG, JOOMLA_PASSWORD) and merge them into the config service.

Also, environment variables can be loaded from .env files, thankfully to symfony/dotenv.

Testing Instructions

1. Create .env file in the site's root directory

2. Set environment variables (inside the .env file):

   JOOMLA_OFFLINE=1
   JOOMLA_OFFLINE_MESSAGE='Joomla!'

3. Reload site's home page and ensure that site is offline and the Joomla! message is shown

4. Run the following command and ensure that the output is true:

   cli/joomla.php config:get offline

5. Run the following command and ensure that the output is Joomla!:

   cli/joomla.php config:get offline_message

Actual result BEFORE applying this Pull Request

All should work.

Expected result AFTER applying this Pull Request

All should work.

Link to documentations

Please select:

• Documentation link for docs.joomla.org:

• No documentation changes for docs.joomla.org needed

• Pull Request link for manual.joomla.org: joomla/Manual#432

• No documentation changes for manual.joomla.org needed

Why?

The 12-factor app methodology recommends to store config in the environment.

Also, it makes Joomla more cloud-friendly and simplifies running it inside containers.

For example, using environment variables it's very easy to configure separate database for testing:

<?xml version="1.0" encoding="UTF-8"?>
<phpunit bootstrap="tests/Unit/bootstrap.php" colors="false">
        <testsuites>
                <testsuite name="Unit">
                        <directory suffix="Test.php">./tests/Unit</directory>
                </testsuite>
                <testsuite name="Integration">
                        <directory suffix="Test.php">./tests/Integration</directory>
                </testsuite>
        </testsuites>
        <php>
                <env name="JOOMLA_DBHOST" value="localhost" force="true"/>
                <env name="JOOMLA_DBNAME" value="joomla_test" force="true" />
                <env name="JOOMLA_DBUSER" value="joomla_test_user" force="true" />
                <env name="JOOMLA_DBPASSWORD" value="joomla_test_password" force="true" />
        </php>
</phpunit>