[Doctrine] Update doctrine.rst on ssl documentation

[lacatoire]

Added SSL configuration example for MySQL in Doctrine DBAL

• Included YAML and XML configuration examples for setting up an SSL connection with MySQL using Doctrine DBAL in Symfony.
• Explained how to use environment variables for specifying SSL certificate paths (MYSQL_SSL_KEY, MYSQL_SSL_CERT, MYSQL_SSL_CA).
• Added a note on configuring the .env.local or .env.local.php files with the appropriate certificate paths.

[lacatoire]

@javiereguiluz I did not succeed squashing, so i've made another PR

[javiereguiluz]

Thanks a lot Louis-Arnaud!

Yes, squashing is sometimes tricky and it's easier to start over. This happened to me many times. So, thanks for the extra effort. Cheers!