Add italian translation

[vadal]

A new translation needs to have three main steps:

First, translate the pages you see here https://github.com/pyladies/global-conference-2025/tree/main/src/pages
Translate all the strings already allocated in https://github.com/pyladies/global-conference-2025/blob/main/src/i18n/ui.ts
Add the language to the configuration file https://github.com/pyladies/global-conference-2025/blob/main/astro.config.mjs