feat: Add announcements system

[beebls]

Please tick as appropriate:

• I have tested this code on a steam deck or on a PC
• My changes generate no new errors/warnings
• This is a bugfix/hotfix
• This is a new feature

If you're wanting to update a translation or add a new one, please use the weblate page: https://weblate.werwolv.net/projects/decky/

Description

This fixes issue: #672

Adds an Announcements (formerly MOTD) display to the root QAM view,

The [plugins/testing].deckbrew.xyz/v1/-/announcements/current endpoint is used, and the latest announcement from this endpoint is display in the QAM.

Upon clicking the X button, that announcement's id is added to a hidden announcements list so that it isn't displayed again

[suchmememanyskill]

Where should people direct feedback?

(Also i assume this shows the first time you use decky? Might want to add something like start with looking at the store)

[RodoMa92]

That's a good point, but there is another blocking issue. The text need to be moved in en-US.json and not hardcoded here.

[TrainDoctor]

Remaining items before merge:

• Announcements must be checked for regularly similar to checks for updates to decky and for plugins.
• Markdown support for URLs etc.
• SteamDeckHomebrew/decky-plugin-store#73
  • Store needs to expose modifiable expiration timeframe that is applied to all announcements by default.
• SteamDeckHomebrew/Plugin-Store-Admin#1
  • Also needs to provide edit field for default announcement expiration timeframe.
• Announcement telling you which store you're on (optional but helpful)
  • Should be able to be disabled for frequent testers etc.
    @beebls, @gbdlin and @AAGaming00: please make sure to coordinate with me so we can get this out asap.