🌐 Add Spanish translation for `docs/es/docs/newsletter.md` (#10922)

docs/es/docs/newsletter.md

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+# Boletín de Noticias de FastAPI y amigos
+
+<iframe data-w-type="embedded" frameborder="0" scrolling="no" marginheight="0" marginwidth="0" src="https://xr4n4.mjt.lu/wgt/xr4n4/hj5/form?c=40a44fa4" width="100%" style="height: 0;"></iframe>
+
+<script type="text/javascript" src="https://app.mailjet.com/pas-nc-embedded-v1.js"></script>