Add default auto translation server in settings [enhancement]

[alltheseas]

User Story

As a new pleb Damus user who would like to communicate with the plebs who speak foreign languages to me, I would like Damus to help me translate foreign languages automagically, so I can increase the understanding of foreign speaking plebs.

Acceptance Criteria

1. Set a ~Libretranslate~ translatio API as default server [currently setting is blank, with option to manually add ~Libretranslate~ server/API]

Related to: Add LibreTranslate integration for machine translating notes from other languages #394 by @tyiu