Autoupdate support for AUR and Flatpak

Nobody has claimed this yet.

## The Issue
We have community maintained builds for [AUR](https://aur.archlinux.org/packages/lbry-app-bin/) and Flatpak(https://flathub.org/apps/details/io.lbry.lbry-app) packages. The current auto update process for Linux only supports Debs and will trigger a download and install even on AUR/Flatpak builds.

This issue to do handle update notifications for AUR and Flatpak installs. The updater could simply tell the user which command to run in order to update when one is available. It should probably look at the version numbers in the respective community maintained repos.

The LBRY team is looking for a community contributor to take on this effort if they feel strongly about supporting additional Linux install processes. It may also be a possibility to work auto update into electron-builder, which only currently supports snaps.

## System Configuration

## Anything Else

## Screenshots

### Acceptance Criteria
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### Definition of Done
- [ ] Tested against acceptance criteria
- [ ] Tested against the assumptions of the user story
- [ ] The project builds without errors
- [ ] Unit tests are written and passing
- [ ] Tests on devices/browsers listed in the issue have passed
- [ ] QA performed & issues resolved
- [ ] Refactoring completed
- [ ] Any configuration or build changes documented
- [ ] Documentation updated
- [ ] Peer Code Review performed

The issue names no files or tests; begin by locating the Linux auto-update path and the Electron packaging configuration, including electron-builder. Compare how AUR and Flatpak versions are discovered and how update commands would be presented; done means those installs receive correct notifications without triggering Debian download/install behavior, with tests and documentation added.

Written by the indexing model from the issue text.