Use app. prefix for parameters

[seb-jean]

I changed the locale setting to put the app. prefix in order to follow best practices.

https://symfony.com/doc/current/best_practices.html#use-short-and-prefixed-parameter-names :

Consider using app. as the prefix of your parameters to avoid collisions with Symfony and third-party bundles/libraries parameters. Then, use just one or two words to describe the purpose of the parameter

[javiereguiluz]

Yes, let's follow our own best practices 🙏

Thanks @seb-jean!