Allow extending upon MySQL client extra configuration

[jissereitsma]

This commit allows for extending the original client configuration (hard-coded) with an optional etc/mysql-client-config.php file) allowing to add or override entries.

Description (*)

By default, the Integration Test Framework generates a file defaults_extra.cnf per sandbox with the following content (in this example, assuming user and password are root):

[client]
user=root
password="root"

Sometimes, it is needed though to extend this configuration. One example here is when you are using a MariaDB client that defaults to TLS/SSL while the MariaDB server is Docker-based and only serving self-generated SSL certificates or worse, not serving SSL at all. In that case, the best way is to disable SSL for the client:

[client]
user=root
password="root"

[client-mariadb]
disable-ssl

This PR allows for an additional file dev/tests/integration/etc/mysql-client-config.php to be created with content like the following:

<?php
return [
    'client-mariadb' => [
        'disable-ssl',
    ],
];

The returned array of this file is merged into the original array and then converted into proper INI output.

Manual testing scenarios (*)

1. Setup a local Magento 2 environment for integration testing with a MariaDB 10.6 database and corresponding MariaDB client (which defaults to using SSL - like 15.2). Run the integration tests. These tests should fail at the moment when maria-dump (aka mysqldump) is dumping the database.

Note that the actual error is normally hidden in the output. However, the Integration Test output might show something to this:

Next Magento\Framework\Exception\LocalizedException: Command returned non-zero exit code:
`mariadb-dump --defaults-file='/tmp/magento/dev/tests/integration/tmp/sandbox-0-01396a4ac7ba2911191f088825c313a54c44dcc0dfa242bbfe20506ac8ed5c75/defaults_extra.cnf' --host='mysql' --port='3306' --no-tablespaces  'magento2' > '/tmp/magento/dev/tests/integration/tmp/sandbox-0-01396a4ac7ba2911191f088825c313a54c44dcc0dfa242bbfe20506ac8ed5c75/setup_dump_magento2.sql' 2>&1` 

Next, running the command mariadb-dump --defaults-file='/var/www/html/dev/tests/integration/tmp/sandbox-0-7541d88ba2b35f337a534b2eac286d8af07070d5588b8583cfd058f6f47e3972/defaults_extra.cnf' --host='mysqltmpfs' --port='3306' --no-tablespaces 'magento2' > '/var/www/html/dev/tests/integration/tmp/sandbox-0-7541d88ba2b35f337a534b2eac286d8af07070d5588b8583cfd058f6f47e3972/setup_dump_magento2.sql manually, will output this SSL error:

mariadb-dump: Got error: 2026: "TLS/SSL error: SSL is required, but the server does not support it" when trying to connect

3. Apply the patch and add a file dev/tests/integration/etc/mysql-client-config.php and rerun the tests. The tests should now succeed.

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• README.md files for modified modules are updated and included in the pull request if any README.md predefined sections require an update
• All automated tests passed successfully (all builds are green)

[m2-assistant]

Hi @jissereitsma. Thank you for your contribution!
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